1. products list

Comparison results

RS3621xs+ RS4021xs+
Hardware Specs
Hardware Specifications
CPU
CPU Model Intel Xeon D-1541 Intel Xeon D-1541
CPU Quantity 1 1
CPU Cores 8 8
CPU Threads 16 16
CPU Architecture 64-bit 64-bit
CPU Frequency 2.1 (base) / 2.7 (turbo) GHz 2.1 (base) / 2.7 (turbo) GHz
Hardware Encryption Engine
Memory
System Memory 8 GB DDR4 ECC UDIMM 16 GB DDR4 ECC UDIMM
Total Memory Slots 4 4
Maximum Memory Capacity 64 GB (16 GB x 4) 64 GB (16 GB x 4)
Notes
  • Synology may revise pre-installed memory module specifications in response to component lifecycle and supply conditions. All revised components undergo the same rigorous validation to ensure equivalent compatibility, stability, and performance.
  • Please select Synology memory modules for optimum compatibility and reliability. Synology will not provide complete product warranty or technical support if non-Synology memory modules are used for memory expansion.
  • For multi-module memory configurations, all modules must be identical and share the same model number. Check the Product Manual of your Synology product for recommended memory configurations.
  • Synology may revise pre-installed memory module specifications in response to component lifecycle and supply conditions. All revised components undergo the same rigorous validation to ensure equivalent compatibility, stability, and performance.
  • Please select Synology memory modules for optimum compatibility and reliability. Synology will not provide complete product warranty or technical support if non-Synology memory modules are used for memory expansion.
  • For multi-module memory configurations, all modules must be identical and share the same model number. Check the Product Manual of your Synology product for recommended memory configurations.
Storage
Drive Bays 12 16
Maximum Drive Bays with Expansion Unit 36 (RX1217 x 2) 40 (RX1217 x 2)
Drive Type (See all supported drives)
  • 3.5" SATA HDD
  • 2.5" SATA SSD
  • 3.5" SATA HDD
  • 2.5" SATA SSD
Hot Swappable Drive*
Notes Synology only guarantees full functionality, reliability, and performance for Synology drives listed on the compatibility list. The use of non-validated components may limit certain functionality and result in data loss and system instability. Synology only guarantees full functionality, reliability, and performance for Synology drives listed on the compatibility list. The use of non-validated components may limit certain functionality and result in data loss and system instability.
External Ports
RJ-45 1GbE LAN Port 4 4
RJ-45 10GbE LAN Port 2 2
USB 3.2 Gen 1 Port 2 2
Expansion Port 2 2
Expansion Port Type Infiniband Infiniband
PCIe
PCIe Expansion 2 x Gen3 x8 slots (x8 link) 2 x Gen3 x8 slots (x8 link)
Appearance
Form Factor (RU) 2U 3U
Size (Height x Width x Depth) 88 mm x 482 mm x 724 mm 132.3 mm x 482 mm x 656.5 mm
Weight 14.5 kg 17.4 kg
Rack Installation Support* 4-post 19" rack (Synology Rail Kit - RKS-02) 4-post 19" rack (Synology Rail Kit - RKS-02)
Notes The rail kit is sold separately The rail kit is sold separately
Others
System Fan 80 mm x 80 mm x 4 pcs 80 mm x 80 mm x 3 pcs
Fan Speed Mode
  • Full-Speed Mode
  • Cool Mode
  • Quiet Mode
  • Full-Speed Mode
  • Cool Mode
  • Quiet Mode
Easy Replacement System Fan
Power Recovery
Noise Level* 50.2 dB(A) 44.7 dB(A)
Scheduled Power On / Off
Wake on LAN / WAN
Power Supply Unit / Adapter 500 watts
550 watts*		 800 watts
550 watts*
Redundant Power Supply
AC Input Power Voltage 100 V to 240 V AC 100 V to 240 V AC
Power Frequency 50/60 Hz, Single Phase 50/60 Hz, Single Phase
Power Consumption 142.5 watts (Access)
72.76 watts (HDD Hibernation)		 145.79 watts (Access)
62.68 watts (HDD Hibernation)
British Thermal Unit 485.93 BTU/hr (Access)
248.11 BTU/hr (HDD Hibernation)		 497.14 BTU/hr (Access)
213.74 BTU/hr (HDD Hibernation)
Notes
  • For more information on how power consumption is measured, refer to this article.
  • Power supply specifications vary by hardware revision. A 500 W PSU is used in devices with serial numbers containing SZR (5th to 7th digits), while a 550 W PSU is in devices with UUR and VR1 serial numbers. For more information, refer to the Product Change Notice.
  • Noise Level Testing Environment: Fully loaded with Seagate 2TB ST2000VN000 hard drive(s) in the idle state. Two G.R.A.S. Type 40AE microphones, each set up 1 meter away from the Synology NAS at the front and rear. Background noise: 16.49-17.51 dB(A); Temperature: 24.25-25.75˚C; Humidity: 58.2-61.8%
  • For more information on how power consumption is measured, refer to this article.
  • Power supply specifications vary by hardware revision. An 800 W PSU is used in devices with serial numbers containing T2R (5th to 7th digits), while a 550 W PSU is in devices with ULR and VR4 serial numbers. For more information, refer to the Product Change Notice.
  • Noise Level Testing Environment: Fully loaded with Seagate 2TB ST2000VN000 hard drive(s) in the idle state. Two G.R.A.S. Type 40AE microphones, each set up 1 meter away from the Synology NAS at the front and rear. Background noise: 16.49-17.51 dB(A); Temperature: 24.25-25.75˚C; Humidity: 58.2-61.8%
Temperature
Operating Temperature 0°C to 35°C (32°F to 95°F) 0°C to 35°C (32°F to 95°F)
Storage Temperature -20°C to 60°C (-5°F to 140°F) -20°C to 60°C (-5°F to 140°F)
Operating Humidity 8% to 80% RH 8% to 80% RH
Storage Humidity 5% to 95% RH 5% to 95% RH
Certification
  • FCC
  • CE
  • BSMI
  • VCCI
  • RCM
  • EAC
  • CCC
  • KC
  • BIS
  • UL
  • FCC
  • CE
  • BSMI
  • VCCI
  • RCM
  • EAC
  • CCC
  • KC
  • BIS
  • UL
Warranty 5 Years 5 Years
Notes The warranty period starts from the purchase date as stated on your purchase receipt. (Learn more) The warranty period starts from the purchase date as stated on your purchase receipt. (Learn more)
Environment RoHS Compliant RoHS Compliant
Packaging Content
  • Main Unit X 1
  • Accessory Pack X 1
  • AC Power Cord X 2
  • Quick Installation Guide X 1
  • Main Unit X 1
  • Accessory Pack X 1
  • AC Power Cord X 2
  • Quick Installation Guide X 1
Optional Accessories
Notes All memory modules will operate at the maximum frequency specified by the CPU manufacturer. All memory modules will operate at the maximum frequency specified by the CPU manufacturer.
Software Specs
DSM Specifications
Storage Management
Maximum Single Volume Size
  • 1 PB (64 GB memory required, for RAID 6 groups only)
  • 200 TB (32 GB memory required)
  • 108 TB
  • 1 PB (64 GB memory required, for RAID 6 groups only)
  • 200 TB (32 GB memory required)
  • 108 TB
Maximum Internal Volume Number 256 256
SSD Read/Write Cache (Determining cache size)
SSD TRIM
RAID Group
Supported RAID Type
  • RAID F1
  • Basic
  • JBOD
  • RAID 0
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
  • RAID F1
  • Basic
  • JBOD
  • RAID 0
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
RAID Migration
  • Basic to RAID 1
  • Basic to RAID 5
  • RAID 1 to RAID 5
  • RAID 5 to RAID 6
  • Basic to RAID 1
  • Basic to RAID 5
  • RAID 1 to RAID 5
  • RAID 5 to RAID 6
Volume Expansion with Larger HDDs
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
Volume Expansion by Adding a HDD
  • RAID F1
  • JBOD
  • RAID 5
  • RAID 6
  • RAID F1
  • JBOD
  • RAID 5
  • RAID 6
Global Hot Spare Supported RAID Type
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
Notes
  • Volumes over 108 TB require 32 GB of memory or more.
  • Certain conditions are required to support a 1 PB volume. Please refer to this article for more information.
  • Actual maximum storage pool and volume sizes vary depending on drives used, the number of drive bays available, and the RAID configuration.
  • Usable capacity for each volume will be lower than the maximum volume size and is dependent on the filesystem and the amount of system metadata stored.
  • Volumes over 108 TB require 32 GB of memory or more.
  • Certain conditions are required to support a 1 PB volume. Please refer to this article for more information.
  • Actual maximum storage pool and volume sizes vary depending on drives used, the number of drive bays available, and the RAID configuration.
  • Usable capacity for each volume will be lower than the maximum volume size and is dependent on the filesystem and the amount of system metadata stored.
File System
Internal Drives
  • Btrfs
  • ext4
  • Btrfs
  • ext4
External Drives
  • Btrfs
  • ext4
  • ext3
  • FAT32
  • NTFS
  • HFS+
  • exFAT
  • Btrfs
  • ext4
  • ext3
  • FAT32
  • NTFS
  • HFS+
  • exFAT
File Services
File Protocol
  • SMB
  • AFP
  • NFS
  • FTP
  • WebDAV
  • Rsync
  • SMB
  • AFP
  • NFS
  • FTP
  • WebDAV
  • Rsync
Maximum Number of SMB Connections (FSCT-Based) 1,300 1,500
Windows Access Control List (ACL) Integration
NFS Kerberos Authentication
Notes
  • Connection value of this model is tested with Synology SATA SSD fully populated and up to four 10GbE network ports
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • SMB performance was evaluated using Microsoft File Server Capacity Tool (FSCT) version 1.3, with the following configuration:
    • Test workload: HomeFolder scenario provided by the FSCT tool
    • Test duration: 600 seconds
    • Domain controller & FSCT controller: Windows Server 2022
    • FSCT clients: 8 × Windows 10 machines
    • SMB feature: Directory leasing enabled
  • Connection value of this model is tested with Synology SATA SSD fully populated and up to four 10GbE network ports
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • SMB performance was evaluated using Microsoft File Server Capacity Tool (FSCT) version 1.3, with the following configuration:
    • Test workload: HomeFolder scenario provided by the FSCT tool
    • Test duration: 600 seconds
    • Domain controller & FSCT controller: Windows Server 2022
    • FSCT clients: 8 × Windows 10 machines
    • SMB feature: Directory leasing enabled
Account & Shared Folder
Maximum Local User Accounts 5,120 5,120
Maximum Local Groups 512 512
Maximum Shared Folder 512 512
Maximum Shared Folder Sync Tasks 32 32
Hybrid Share
Hybrid Share Folder Number 15 15
Hyper Backup
Folder and Package Backup
Entire System Backup
Notes Full-system backup requires DSM 7.2 or later. Full-system backup requires DSM 7.2 or later.
High Availability
Synology High Availability
Log Center
Syslog Events per Second 3,000 3,000
Virtualization
VMware vSphere ESXi 8.0 U2, ESXi 8.0 U1, ESXi 8.0, ESXi 7.0 U3, ESXi 7.0 U2, ESXi 7.0 U1, ESXi 7.0, ESXi 6.7 U3, ESXi 6.7 U2, ESXi 6.7 U1, ESXi 6.7, ESXi 6.5 U3, ESXi 6.5 U2, ESXi 6.5 U1, ESXi 6.5 ESXi 8.0 U2, ESXi 8.0 U1, ESXi 8.0, ESXi 7.0 U3, ESXi 7.0 U2, ESXi 7.0 U1, ESXi 7.0, ESXi 6.7 U3, ESXi 6.7 U2, ESXi 6.7 U1, ESXi 6.7, ESXi 6.5 U3, ESXi 6.5 U2, ESXi 6.5 U1, ESXi 6.5
Microsoft Hyper-V Windows Server 2022, Windows Server 2019, Windows Server 2016 Windows Server 2022, Windows Server 2019, Windows Server 2016
Citrix XenServer XenServer 8, Citrix Hypervisor 8.2 LTSR CU1 XenServer 8, Citrix Hypervisor 8.2 LTSR CU1
OpenStack Cinder Cinder
General Specifications
Supported Protocols SMB1 (CIFS), SMB2, SMB3, NFSv3, NFSv4, NFSv4.1, NFS Kerberized sessions, iSCSI, Fibre Channel, HTTP, HTTPs, FTP, SNMP, LDAP, CalDAV SMB1 (CIFS), SMB2, SMB3, NFSv3, NFSv4, NFSv4.1, NFS Kerberized sessions, iSCSI, Fibre Channel, HTTP, HTTPs, FTP, SNMP, LDAP, CalDAV
Supported Browsers
  • Chrome
  • Firefox
  • Edge
  • Safari
  • Chrome
  • Firefox
  • Edge
  • Safari
Supported Language English, Deutsch, Français, Italiano, Español, Dansk, Norsk, Svenska, Nederlands, Русский, Polski, Magyar, Português do Brasil, Português Europeu, Türkçe, Český, ภาษาไทย, 日本語, 한국어, 繁體中文, 简体中文 English, Deutsch, Français, Italiano, Español, Dansk, Norsk, Svenska, Nederlands, Русский, Polski, Magyar, Português do Brasil, Português Europeu, Türkçe, Český, ภาษาไทย, 日本語, 한국어, 繁體中文, 简体中文
Notes For an updated list of supported browser versions, check the DSM Technical Specifications. For an updated list of supported browser versions, check the DSM Technical Specifications.
Add-on Packages view the complete package list
Central Management System
Synology AI Console
Third-Party AI Model Integration
Maximum De-Identification Rate 1,300 words per second 1,500 words per second
Notes
  • De-identification performance measurement: Filters for Credit Card Numbers, IBAN, Individual Taxpayer Identification Number, SSN, and Names applied to a 4,355-word English text.
  • To enable de-identification, your device must have at least 8 GB of memory and Container Manager installed.
  • De-identification performance measurement: Filters for Credit Card Numbers, IBAN, Individual Taxpayer Identification Number, SSN, and Names applied to a 4,355-word English text.
  • To enable de-identification, your device must have at least 8 GB of memory and Container Manager installed.
Synology Chat
Maximum Number of Users 500 500
Notes
  • Measured with simulated users, each with an average record of 20,000 messages, emojis, or stickers. The required server response time is below ten seconds.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Measured with simulated users, each with an average record of 20,000 messages, emojis, or stickers. The required server response time is below ten seconds.
  • Models with expandable memory are tested with the maximum supported quantity installed.
Download Station
Maximum Concurrent Download Tasks 80 80
SAN Manager
Maximum iSCSI Target Number 128 128
Maximum LUN 256 256
LUN Clone/Snapshot, Windows ODX
Synology MailPlus / MailPlus Server
Free Email Accounts 5 (Additional accounts require purchase of licenses) 5 (Additional accounts require purchase of licenses)
Maximum Number of Users 2,800 3,200
Notes
  • The suggested maximum number of users is based on the following workload: 20% of users with a 20,000 item mailbox randomly performing actions and receiving 240 emails per day, and 80% of users receiving 20 emails per day. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed. Learn more about memory requirements.
  • Operating in high-availability mode will incur additional overhead.
  • Features enabled during evaluation: anti-spam, anti-virus, DNSBL, greylist, content scanning, and full-text search (English).
  • The suggested maximum number of users is based on the following workload: 20% of users with a 20,000 item mailbox randomly performing actions and receiving 240 emails per day, and 80% of users receiving 20 emails per day. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed. Learn more about memory requirements.
  • Operating in high-availability mode will incur additional overhead.
  • Features enabled during evaluation: anti-spam, anti-virus, DNSBL, greylist, content scanning, and full-text search (English).
Media Server
DLNA Compliance
Synology Photos
Facial Recognition
Object Recognition
Snapshot Replication
Maximum Snapshots per Shared Folder 512 512
Maximum Snapshots per LUN 128 128
Maximum Snapshots per System 16,384 16,384
Maximum Replication Tasks for Shared Folders 64 64
Maximum Replication Tasks for LUNs 32 32
Maximum Replication Tasks per System 64 64
Surveillance Station
Default Licenses 2 (Additional cameras require purchase of licenses) 2 (Additional cameras require purchase of licenses)
Maximum IP Cameras and Total FPS (H.264)
  • 1080p: 90 channels, 2250 FPS
  • 3M: 90 channels, 1500 FPS
  • 5M: 90 channels, 900 FPS
  • 4K: 55 channels, 550 FPS
  • 1080p: 280 channels, 2800 FPS
  • 3M: 200 channels, 2000 FPS
  • 5M: 120 channels, 1200 FPS
  • 4K: 85 channels, 850 FPS
Maximum IP Cameras and Total FPS (H.265)
  • 1080p: 90 channels, 2700 FPS
  • 3M: 90 channels, 2250 FPS
  • 5M: 90 channels, 1500 FPS
  • 4K: 90 channels, 1080 FPS
  • 1080p: 285 channels, 8550 FPS
  • 3M: 280 channels, 2800 FPS
  • 5M: 200 channels, 2000 FPS
  • 4K: 120 channels, 1200 FPS
Notes
  • Performance figures are obtained from testing conducted with the device fully populated with drives, with their default memory configuration, and under a continuous recording setup. Actual system capabilities may vary based on configuration, drive performance, enabled features, and the presence of additional workloads.
  • Use NVR Selector to quickly find a suitable model based on your requirements.
  • The number of video channels that can be viewed simultaneously is double the maximum number of cameras for the same codec and resolution.
  • Surveillance Station 9.1.3 or above is required to support the maximum IP cameras and FPS figures listed.
  • Performance figures are obtained from testing conducted with the device fully populated with drives, with their default memory configuration, and under a continuous recording setup. Actual system capabilities may vary based on configuration, drive performance, enabled features, and the presence of additional workloads.
  • Use NVR Selector to quickly find a suitable model based on your requirements.
  • The number of video channels that can be viewed simultaneously is double the maximum number of cameras for the same codec and resolution.
Synology Drive
Maximum Number of Users 2,400 2,700
Maximum Number of Hosted Files 15,000,000 (applies to files indexed or hosted by Synology Drive. For file access through other standard protocols, refer to the File Services section above) 25,000,000 (applies to files indexed or hosted by Synology Drive. For file access through other standard protocols, refer to the File Services section above)
Notes
  • The suggested maximum number of users is based on the following workload: 20% of users randomly perform file operations (upload, download, move, and delete), and 80% of users are logged in but idle. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Exceeding the recommended numbers above will not block application operations, but may result in longer response time.
  • Btrfs file system and non-encrypted shared folders were used during the aforementioned testing.
  • The suggested maximum number of users is based on the following workload: 20% of users randomly perform file operations (upload, download, move, and delete), and 80% of users are logged in but idle. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Exceeding the recommended numbers above will not block application operations, but may result in longer response time.
  • Btrfs file system and non-encrypted shared folders were used during the aforementioned testing.
Synology Office
Maximum Number of Users 2,300 2,700
Notes
  • The suggested maximum number of users is based on the following workload: 20% of users are executing random actions at an average of 30-second intervals, and 80% of users are logged in and viewing a file. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Client performance may affect maximum simultaneous editing users. Client PCs used for testing: Intel Core i3-3220 / 8GB RAM
  • The suggested maximum number of users is based on the following workload: 20% of users are executing random actions at an average of 30-second intervals, and 80% of users are logged in and viewing a file. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Client performance may affect maximum simultaneous editing users. Client PCs used for testing: Intel Core i3-3220 / 8GB RAM
Virtual Machine Manager
Recommended Virtual Machine Instances 16 (Learn more) 16 (Learn more)
Recommended Virtual DSM Number (Licenses required) 16 (including 1 Free License) 16 (including 1 Free License)
Notes The specifications vary depending on system configuration and memory size. The specifications vary depending on system configuration and memory size.
VPN Server
Maximum Connections 32 32
Hardware Specs
Hardware Specifications
CPU
CPU Model
RS3621xs+ Intel Xeon D-1541
RS4021xs+ Intel Xeon D-1541
CPU Quantity
RS3621xs+ 1
RS4021xs+ 1
CPU Cores
RS3621xs+ 8
RS4021xs+ 8
CPU Threads
RS3621xs+ 16
RS4021xs+ 16
CPU Architecture
RS3621xs+ 64-bit
RS4021xs+ 64-bit
CPU Frequency
RS3621xs+ 2.1 (base) / 2.7 (turbo) GHz
RS4021xs+ 2.1 (base) / 2.7 (turbo) GHz
Hardware Encryption Engine
RS3621xs+
RS4021xs+
Memory
System Memory
RS3621xs+ 8 GB DDR4 ECC UDIMM
RS4021xs+ 16 GB DDR4 ECC UDIMM
Total Memory Slots
RS3621xs+ 4
RS4021xs+ 4
Maximum Memory Capacity
RS3621xs+ 64 GB (16 GB x 4)
RS4021xs+ 64 GB (16 GB x 4)
Notes
RS3621xs+
  • Synology may revise pre-installed memory module specifications in response to component lifecycle and supply conditions. All revised components undergo the same rigorous validation to ensure equivalent compatibility, stability, and performance.
  • Please select Synology memory modules for optimum compatibility and reliability. Synology will not provide complete product warranty or technical support if non-Synology memory modules are used for memory expansion.
  • For multi-module memory configurations, all modules must be identical and share the same model number. Check the Product Manual of your Synology product for recommended memory configurations.
RS4021xs+
  • Synology may revise pre-installed memory module specifications in response to component lifecycle and supply conditions. All revised components undergo the same rigorous validation to ensure equivalent compatibility, stability, and performance.
  • Please select Synology memory modules for optimum compatibility and reliability. Synology will not provide complete product warranty or technical support if non-Synology memory modules are used for memory expansion.
  • For multi-module memory configurations, all modules must be identical and share the same model number. Check the Product Manual of your Synology product for recommended memory configurations.
Storage
Drive Bays
RS3621xs+ 12
RS4021xs+ 16
Maximum Drive Bays with Expansion Unit
RS3621xs+ 36 (RX1217 x 2)
RS4021xs+ 40 (RX1217 x 2)
Drive Type (See all supported drives)
RS3621xs+
  • 3.5" SATA HDD
  • 2.5" SATA SSD
RS4021xs+
  • 3.5" SATA HDD
  • 2.5" SATA SSD
Hot Swappable Drive*
RS3621xs+
RS4021xs+
Notes
RS3621xs+ Synology only guarantees full functionality, reliability, and performance for Synology drives listed on the compatibility list. The use of non-validated components may limit certain functionality and result in data loss and system instability.
RS4021xs+ Synology only guarantees full functionality, reliability, and performance for Synology drives listed on the compatibility list. The use of non-validated components may limit certain functionality and result in data loss and system instability.
External Ports
RJ-45 1GbE LAN Port
RS3621xs+ 4
RS4021xs+ 4
RJ-45 10GbE LAN Port
RS3621xs+ 2
RS4021xs+ 2
USB 3.2 Gen 1 Port
RS3621xs+ 2
RS4021xs+ 2
Expansion Port
RS3621xs+ 2
RS4021xs+ 2
Expansion Port Type
RS3621xs+ Infiniband
RS4021xs+ Infiniband
PCIe
PCIe Expansion
RS3621xs+ 2 x Gen3 x8 slots (x8 link)
RS4021xs+ 2 x Gen3 x8 slots (x8 link)
Appearance
Form Factor (RU)
RS3621xs+ 2U
RS4021xs+ 3U
Size (Height x Width x Depth)
RS3621xs+ 88 mm x 482 mm x 724 mm
RS4021xs+ 132.3 mm x 482 mm x 656.5 mm
Weight
RS3621xs+ 14.5 kg
RS4021xs+ 17.4 kg
Rack Installation Support*
RS3621xs+ 4-post 19" rack (Synology Rail Kit - RKS-02)
RS4021xs+ 4-post 19" rack (Synology Rail Kit - RKS-02)
Notes
RS3621xs+ The rail kit is sold separately
RS4021xs+ The rail kit is sold separately
Others
System Fan
RS3621xs+ 80 mm x 80 mm x 4 pcs
RS4021xs+ 80 mm x 80 mm x 3 pcs
Fan Speed Mode
RS3621xs+
  • Full-Speed Mode
  • Cool Mode
  • Quiet Mode
RS4021xs+
  • Full-Speed Mode
  • Cool Mode
  • Quiet Mode
Easy Replacement System Fan
RS3621xs+
RS4021xs+
Power Recovery
RS3621xs+
RS4021xs+
Noise Level*
RS3621xs+ 50.2 dB(A)
RS4021xs+ 44.7 dB(A)
Scheduled Power On / Off
RS3621xs+
RS4021xs+
Wake on LAN / WAN
RS3621xs+
RS4021xs+
Power Supply Unit / Adapter
RS3621xs+ 500 watts
550 watts*
RS4021xs+ 800 watts
550 watts*
Redundant Power Supply
RS3621xs+
RS4021xs+
AC Input Power Voltage
RS3621xs+ 100 V to 240 V AC
RS4021xs+ 100 V to 240 V AC
Power Frequency
RS3621xs+ 50/60 Hz, Single Phase
RS4021xs+ 50/60 Hz, Single Phase
Power Consumption
RS3621xs+ 142.5 watts (Access)
72.76 watts (HDD Hibernation)
RS4021xs+ 145.79 watts (Access)
62.68 watts (HDD Hibernation)
British Thermal Unit
RS3621xs+ 485.93 BTU/hr (Access)
248.11 BTU/hr (HDD Hibernation)
RS4021xs+ 497.14 BTU/hr (Access)
213.74 BTU/hr (HDD Hibernation)
Notes
RS3621xs+
  • For more information on how power consumption is measured, refer to this article.
  • Power supply specifications vary by hardware revision. A 500 W PSU is used in devices with serial numbers containing SZR (5th to 7th digits), while a 550 W PSU is in devices with UUR and VR1 serial numbers. For more information, refer to the Product Change Notice.
  • Noise Level Testing Environment: Fully loaded with Seagate 2TB ST2000VN000 hard drive(s) in the idle state. Two G.R.A.S. Type 40AE microphones, each set up 1 meter away from the Synology NAS at the front and rear. Background noise: 16.49-17.51 dB(A); Temperature: 24.25-25.75˚C; Humidity: 58.2-61.8%
RS4021xs+
  • For more information on how power consumption is measured, refer to this article.
  • Power supply specifications vary by hardware revision. An 800 W PSU is used in devices with serial numbers containing T2R (5th to 7th digits), while a 550 W PSU is in devices with ULR and VR4 serial numbers. For more information, refer to the Product Change Notice.
  • Noise Level Testing Environment: Fully loaded with Seagate 2TB ST2000VN000 hard drive(s) in the idle state. Two G.R.A.S. Type 40AE microphones, each set up 1 meter away from the Synology NAS at the front and rear. Background noise: 16.49-17.51 dB(A); Temperature: 24.25-25.75˚C; Humidity: 58.2-61.8%
Temperature
Operating Temperature
RS3621xs+ 0°C to 35°C (32°F to 95°F)
RS4021xs+ 0°C to 35°C (32°F to 95°F)
Storage Temperature
RS3621xs+ -20°C to 60°C (-5°F to 140°F)
RS4021xs+ -20°C to 60°C (-5°F to 140°F)
Operating Humidity
RS3621xs+ 8% to 80% RH
RS4021xs+ 8% to 80% RH
Storage Humidity
RS3621xs+ 5% to 95% RH
RS4021xs+ 5% to 95% RH
Certification
RS3621xs+
  • FCC
  • CE
  • BSMI
  • VCCI
  • RCM
  • EAC
  • CCC
  • KC
  • BIS
  • UL
RS4021xs+
  • FCC
  • CE
  • BSMI
  • VCCI
  • RCM
  • EAC
  • CCC
  • KC
  • BIS
  • UL
Warranty
RS3621xs+ 5 Years
RS4021xs+ 5 Years
Notes
RS3621xs+ The warranty period starts from the purchase date as stated on your purchase receipt. (Learn more)
RS4021xs+ The warranty period starts from the purchase date as stated on your purchase receipt. (Learn more)
Environment
RS3621xs+ RoHS Compliant
RS4021xs+ RoHS Compliant
Packaging Content
RS3621xs+
  • Main Unit X 1
  • Accessory Pack X 1
  • AC Power Cord X 2
  • Quick Installation Guide X 1
RS4021xs+
  • Main Unit X 1
  • Accessory Pack X 1
  • AC Power Cord X 2
  • Quick Installation Guide X 1
Optional Accessories
RS3621xs+
RS4021xs+
Notes
RS3621xs+ All memory modules will operate at the maximum frequency specified by the CPU manufacturer.
RS4021xs+ All memory modules will operate at the maximum frequency specified by the CPU manufacturer.
Software Specs
DSM Specifications
Storage Management
Maximum Single Volume Size
RS3621xs+
  • 1 PB (64 GB memory required, for RAID 6 groups only)
  • 200 TB (32 GB memory required)
  • 108 TB
RS4021xs+
  • 1 PB (64 GB memory required, for RAID 6 groups only)
  • 200 TB (32 GB memory required)
  • 108 TB
Maximum Internal Volume Number
RS3621xs+ 256
RS4021xs+ 256
SSD Read/Write Cache (Determining cache size)
RS3621xs+
RS4021xs+
SSD TRIM
RS3621xs+
RS4021xs+
RAID Group
RS3621xs+
RS4021xs+
Supported RAID Type
RS3621xs+
  • RAID F1
  • Basic
  • JBOD
  • RAID 0
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
RS4021xs+
  • RAID F1
  • Basic
  • JBOD
  • RAID 0
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
RAID Migration
RS3621xs+
  • Basic to RAID 1
  • Basic to RAID 5
  • RAID 1 to RAID 5
  • RAID 5 to RAID 6
RS4021xs+
  • Basic to RAID 1
  • Basic to RAID 5
  • RAID 1 to RAID 5
  • RAID 5 to RAID 6
Volume Expansion with Larger HDDs
RS3621xs+
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
RS4021xs+
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
Volume Expansion by Adding a HDD
RS3621xs+
  • RAID F1
  • JBOD
  • RAID 5
  • RAID 6
RS4021xs+
  • RAID F1
  • JBOD
  • RAID 5
  • RAID 6
Global Hot Spare Supported RAID Type
RS3621xs+
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
RS4021xs+
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
Notes
RS3621xs+
  • Volumes over 108 TB require 32 GB of memory or more.
  • Certain conditions are required to support a 1 PB volume. Please refer to this article for more information.
  • Actual maximum storage pool and volume sizes vary depending on drives used, the number of drive bays available, and the RAID configuration.
  • Usable capacity for each volume will be lower than the maximum volume size and is dependent on the filesystem and the amount of system metadata stored.
RS4021xs+
  • Volumes over 108 TB require 32 GB of memory or more.
  • Certain conditions are required to support a 1 PB volume. Please refer to this article for more information.
  • Actual maximum storage pool and volume sizes vary depending on drives used, the number of drive bays available, and the RAID configuration.
  • Usable capacity for each volume will be lower than the maximum volume size and is dependent on the filesystem and the amount of system metadata stored.
File System
Internal Drives
RS3621xs+
  • Btrfs
  • ext4
RS4021xs+
  • Btrfs
  • ext4
External Drives
RS3621xs+
  • Btrfs
  • ext4
  • ext3
  • FAT32
  • NTFS
  • HFS+
  • exFAT
RS4021xs+
  • Btrfs
  • ext4
  • ext3
  • FAT32
  • NTFS
  • HFS+
  • exFAT
File Services
File Protocol
RS3621xs+
  • SMB
  • AFP
  • NFS
  • FTP
  • WebDAV
  • Rsync
RS4021xs+
  • SMB
  • AFP
  • NFS
  • FTP
  • WebDAV
  • Rsync
Maximum Number of SMB Connections (FSCT-Based)
RS3621xs+ 1,300
RS4021xs+ 1,500
Windows Access Control List (ACL) Integration
RS3621xs+
RS4021xs+
NFS Kerberos Authentication
RS3621xs+
RS4021xs+
Notes
RS3621xs+
  • Connection value of this model is tested with Synology SATA SSD fully populated and up to four 10GbE network ports
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • SMB performance was evaluated using Microsoft File Server Capacity Tool (FSCT) version 1.3, with the following configuration:
    • Test workload: HomeFolder scenario provided by the FSCT tool
    • Test duration: 600 seconds
    • Domain controller & FSCT controller: Windows Server 2022
    • FSCT clients: 8 × Windows 10 machines
    • SMB feature: Directory leasing enabled
RS4021xs+
  • Connection value of this model is tested with Synology SATA SSD fully populated and up to four 10GbE network ports
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • SMB performance was evaluated using Microsoft File Server Capacity Tool (FSCT) version 1.3, with the following configuration:
    • Test workload: HomeFolder scenario provided by the FSCT tool
    • Test duration: 600 seconds
    • Domain controller & FSCT controller: Windows Server 2022
    • FSCT clients: 8 × Windows 10 machines
    • SMB feature: Directory leasing enabled
Account & Shared Folder
Maximum Local User Accounts
RS3621xs+ 5,120
RS4021xs+ 5,120
Maximum Local Groups
RS3621xs+ 512
RS4021xs+ 512
Maximum Shared Folder
RS3621xs+ 512
RS4021xs+ 512
Maximum Shared Folder Sync Tasks
RS3621xs+ 32
RS4021xs+ 32
Hybrid Share
Hybrid Share Folder Number
RS3621xs+ 15
RS4021xs+ 15
Hyper Backup
Folder and Package Backup
RS3621xs+
RS4021xs+
Entire System Backup
RS3621xs+
RS4021xs+
Notes
RS3621xs+ Full-system backup requires DSM 7.2 or later.
RS4021xs+ Full-system backup requires DSM 7.2 or later.
High Availability
Synology High Availability
RS3621xs+
RS4021xs+
Log Center
RS3621xs+
RS4021xs+
Syslog Events per Second
RS3621xs+ 3,000
RS4021xs+ 3,000
Virtualization
VMware vSphere
RS3621xs+ ESXi 8.0 U2, ESXi 8.0 U1, ESXi 8.0, ESXi 7.0 U3, ESXi 7.0 U2, ESXi 7.0 U1, ESXi 7.0, ESXi 6.7 U3, ESXi 6.7 U2, ESXi 6.7 U1, ESXi 6.7, ESXi 6.5 U3, ESXi 6.5 U2, ESXi 6.5 U1, ESXi 6.5
RS4021xs+ ESXi 8.0 U2, ESXi 8.0 U1, ESXi 8.0, ESXi 7.0 U3, ESXi 7.0 U2, ESXi 7.0 U1, ESXi 7.0, ESXi 6.7 U3, ESXi 6.7 U2, ESXi 6.7 U1, ESXi 6.7, ESXi 6.5 U3, ESXi 6.5 U2, ESXi 6.5 U1, ESXi 6.5
Microsoft Hyper-V
RS3621xs+ Windows Server 2022, Windows Server 2019, Windows Server 2016
RS4021xs+ Windows Server 2022, Windows Server 2019, Windows Server 2016
Citrix XenServer
RS3621xs+ XenServer 8, Citrix Hypervisor 8.2 LTSR CU1
RS4021xs+ XenServer 8, Citrix Hypervisor 8.2 LTSR CU1
OpenStack
RS3621xs+ Cinder
RS4021xs+ Cinder
General Specifications
Supported Protocols
RS3621xs+ SMB1 (CIFS), SMB2, SMB3, NFSv3, NFSv4, NFSv4.1, NFS Kerberized sessions, iSCSI, Fibre Channel, HTTP, HTTPs, FTP, SNMP, LDAP, CalDAV
RS4021xs+ SMB1 (CIFS), SMB2, SMB3, NFSv3, NFSv4, NFSv4.1, NFS Kerberized sessions, iSCSI, Fibre Channel, HTTP, HTTPs, FTP, SNMP, LDAP, CalDAV
Supported Browsers
RS3621xs+
  • Chrome
  • Firefox
  • Edge
  • Safari
RS4021xs+
  • Chrome
  • Firefox
  • Edge
  • Safari
Supported Language
RS3621xs+ English, Deutsch, Français, Italiano, Español, Dansk, Norsk, Svenska, Nederlands, Русский, Polski, Magyar, Português do Brasil, Português Europeu, Türkçe, Český, ภาษาไทย, 日本語, 한국어, 繁體中文, 简体中文
RS4021xs+ English, Deutsch, Français, Italiano, Español, Dansk, Norsk, Svenska, Nederlands, Русский, Polski, Magyar, Português do Brasil, Português Europeu, Türkçe, Český, ภาษาไทย, 日本語, 한국어, 繁體中文, 简体中文
Notes
RS3621xs+ For an updated list of supported browser versions, check the DSM Technical Specifications.
RS4021xs+ For an updated list of supported browser versions, check the DSM Technical Specifications.
Add-on Packages view the complete package list
Central Management System
RS3621xs+
RS4021xs+
Synology AI Console
RS3621xs+
RS4021xs+
Third-Party AI Model Integration
RS3621xs+
RS4021xs+
Maximum De-Identification Rate
RS3621xs+ 1,300 words per second
RS4021xs+ 1,500 words per second
Notes
RS3621xs+
  • De-identification performance measurement: Filters for Credit Card Numbers, IBAN, Individual Taxpayer Identification Number, SSN, and Names applied to a 4,355-word English text.
  • To enable de-identification, your device must have at least 8 GB of memory and Container Manager installed.
RS4021xs+
  • De-identification performance measurement: Filters for Credit Card Numbers, IBAN, Individual Taxpayer Identification Number, SSN, and Names applied to a 4,355-word English text.
  • To enable de-identification, your device must have at least 8 GB of memory and Container Manager installed.
Synology Chat
RS3621xs+
RS4021xs+
Maximum Number of Users
RS3621xs+ 500
RS4021xs+ 500
Notes
RS3621xs+
  • Measured with simulated users, each with an average record of 20,000 messages, emojis, or stickers. The required server response time is below ten seconds.
  • Models with expandable memory are tested with the maximum supported quantity installed.
RS4021xs+
  • Measured with simulated users, each with an average record of 20,000 messages, emojis, or stickers. The required server response time is below ten seconds.
  • Models with expandable memory are tested with the maximum supported quantity installed.
Download Station
RS3621xs+
RS4021xs+
Maximum Concurrent Download Tasks
RS3621xs+ 80
RS4021xs+ 80
SAN Manager
RS3621xs+
RS4021xs+
Maximum iSCSI Target Number
RS3621xs+ 128
RS4021xs+ 128
Maximum LUN
RS3621xs+ 256
RS4021xs+ 256
LUN Clone/Snapshot, Windows ODX
RS3621xs+
RS4021xs+
Synology MailPlus / MailPlus Server
RS3621xs+
RS4021xs+
Free Email Accounts
RS3621xs+ 5 (Additional accounts require purchase of licenses)
RS4021xs+ 5 (Additional accounts require purchase of licenses)
Maximum Number of Users
RS3621xs+ 2,800
RS4021xs+ 3,200
Notes
RS3621xs+
  • The suggested maximum number of users is based on the following workload: 20% of users with a 20,000 item mailbox randomly performing actions and receiving 240 emails per day, and 80% of users receiving 20 emails per day. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed. Learn more about memory requirements.
  • Operating in high-availability mode will incur additional overhead.
  • Features enabled during evaluation: anti-spam, anti-virus, DNSBL, greylist, content scanning, and full-text search (English).
RS4021xs+
  • The suggested maximum number of users is based on the following workload: 20% of users with a 20,000 item mailbox randomly performing actions and receiving 240 emails per day, and 80% of users receiving 20 emails per day. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed. Learn more about memory requirements.
  • Operating in high-availability mode will incur additional overhead.
  • Features enabled during evaluation: anti-spam, anti-virus, DNSBL, greylist, content scanning, and full-text search (English).
Media Server
RS3621xs+
RS4021xs+
DLNA Compliance
RS3621xs+
RS4021xs+
Synology Photos
RS3621xs+
RS4021xs+
Facial Recognition
RS3621xs+
RS4021xs+
Object Recognition
RS3621xs+
RS4021xs+
Snapshot Replication
RS3621xs+
RS4021xs+
Maximum Snapshots per Shared Folder
RS3621xs+ 512
RS4021xs+ 512
Maximum Snapshots per LUN
RS3621xs+ 128
RS4021xs+ 128
Maximum Snapshots per System
RS3621xs+ 16,384
RS4021xs+ 16,384
Maximum Replication Tasks for Shared Folders
RS3621xs+ 64
RS4021xs+ 64
Maximum Replication Tasks for LUNs
RS3621xs+ 32
RS4021xs+ 32
Maximum Replication Tasks per System
RS3621xs+ 64
RS4021xs+ 64
Surveillance Station
RS3621xs+
RS4021xs+
Default Licenses
RS3621xs+ 2 (Additional cameras require purchase of licenses)
RS4021xs+ 2 (Additional cameras require purchase of licenses)
Maximum IP Cameras and Total FPS (H.264)
RS3621xs+
  • 1080p: 90 channels, 2250 FPS
  • 3M: 90 channels, 1500 FPS
  • 5M: 90 channels, 900 FPS
  • 4K: 55 channels, 550 FPS
RS4021xs+
  • 1080p: 280 channels, 2800 FPS
  • 3M: 200 channels, 2000 FPS
  • 5M: 120 channels, 1200 FPS
  • 4K: 85 channels, 850 FPS
Maximum IP Cameras and Total FPS (H.265)
RS3621xs+
  • 1080p: 90 channels, 2700 FPS
  • 3M: 90 channels, 2250 FPS
  • 5M: 90 channels, 1500 FPS
  • 4K: 90 channels, 1080 FPS
RS4021xs+
  • 1080p: 285 channels, 8550 FPS
  • 3M: 280 channels, 2800 FPS
  • 5M: 200 channels, 2000 FPS
  • 4K: 120 channels, 1200 FPS
Notes
RS3621xs+
  • Performance figures are obtained from testing conducted with the device fully populated with drives, with their default memory configuration, and under a continuous recording setup. Actual system capabilities may vary based on configuration, drive performance, enabled features, and the presence of additional workloads.
  • Use NVR Selector to quickly find a suitable model based on your requirements.
  • The number of video channels that can be viewed simultaneously is double the maximum number of cameras for the same codec and resolution.
RS4021xs+
  • Surveillance Station 9.1.3 or above is required to support the maximum IP cameras and FPS figures listed.
  • Performance figures are obtained from testing conducted with the device fully populated with drives, with their default memory configuration, and under a continuous recording setup. Actual system capabilities may vary based on configuration, drive performance, enabled features, and the presence of additional workloads.
  • Use NVR Selector to quickly find a suitable model based on your requirements.
  • The number of video channels that can be viewed simultaneously is double the maximum number of cameras for the same codec and resolution.
Synology Drive
RS3621xs+
RS4021xs+
Maximum Number of Users
RS3621xs+ 2,400
RS4021xs+ 2,700
Maximum Number of Hosted Files
RS3621xs+ 15,000,000 (applies to files indexed or hosted by Synology Drive. For file access through other standard protocols, refer to the File Services section above)
RS4021xs+ 25,000,000 (applies to files indexed or hosted by Synology Drive. For file access through other standard protocols, refer to the File Services section above)
Notes
RS3621xs+
  • The suggested maximum number of users is based on the following workload: 20% of users randomly perform file operations (upload, download, move, and delete), and 80% of users are logged in but idle. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Exceeding the recommended numbers above will not block application operations, but may result in longer response time.
  • Btrfs file system and non-encrypted shared folders were used during the aforementioned testing.
RS4021xs+
  • The suggested maximum number of users is based on the following workload: 20% of users randomly perform file operations (upload, download, move, and delete), and 80% of users are logged in but idle. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Exceeding the recommended numbers above will not block application operations, but may result in longer response time.
  • Btrfs file system and non-encrypted shared folders were used during the aforementioned testing.
Synology Office
RS3621xs+
RS4021xs+
Maximum Number of Users
RS3621xs+ 2,300
RS4021xs+ 2,700
Notes
RS3621xs+
  • The suggested maximum number of users is based on the following workload: 20% of users are executing random actions at an average of 30-second intervals, and 80% of users are logged in and viewing a file. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Client performance may affect maximum simultaneous editing users. Client PCs used for testing: Intel Core i3-3220 / 8GB RAM
RS4021xs+
  • The suggested maximum number of users is based on the following workload: 20% of users are executing random actions at an average of 30-second intervals, and 80% of users are logged in and viewing a file. Learn more
  • Models with SSD support are tested with a single SSD volume.
  • Models with expandable memory are tested with the maximum supported quantity installed.
  • Client performance may affect maximum simultaneous editing users. Client PCs used for testing: Intel Core i3-3220 / 8GB RAM
Virtual Machine Manager
RS3621xs+
RS4021xs+
Recommended Virtual Machine Instances
RS3621xs+ 16 (Learn more)
RS4021xs+ 16 (Learn more)
Recommended Virtual DSM Number (Licenses required)
RS3621xs+ 16 (including 1 Free License)
RS4021xs+ 16 (including 1 Free License)
Notes
RS3621xs+ The specifications vary depending on system configuration and memory size.
RS4021xs+ The specifications vary depending on system configuration and memory size.
VPN Server
RS3621xs+
RS4021xs+
Maximum Connections
RS3621xs+ 32
RS4021xs+ 32