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RackStation RS4021xs+

Enterprise NAS with built-in service continuity engineered for data-intensive applications.

Works best with Synology drives

Engineered to handle intensive 24/7 workloads, Synology drives consistently deliver top-grade performance.

Powered by Synology DiskStation Manager

The RS4021xs+ runs Synology DiskStation Manager (DSM), the web-based operating system equipped with powerful applications and services for business.

Central Management System

Conveniently manage your fleet of Synology NAS from a centralized console.

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Synology Drive

Instantly access your NAS files across multiple devices whenever you want, wherever you are.

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Collaboration Suite

Satisfy all team collaboration needs behind the safety of your own private cloud with Synology Office, Calendar, and Chat.

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Virtual Machine Manager

Run various operating systems in isolated sandboxes. Seamlessly clone, store, and migrate virtual machines.

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Security

Secure data with comprehensive built-in security tools to protect your devices against evolving threats.

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Public Cloud Integration

Back up and synchronize data easily between public cloud accounts and your NAS.

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  • 1 Power button and indicator
  • 2 Alert Off Button
  • 3 Drive tray
  • 4 Drive status indicator
  • 5 PSU fan
  • 6 Power Port
  • 7 PSU Indicators & Alert Off Buttons
  • 8 Console port
  • 9 1GbE/10GbE RJ-45 Ports
  • 10 USB 3.2 Ports
  • 11 Expansion port
  • 12 PCIe expansion slot
  • 13 Reset button

Notes:

  1. Performance testing conducted by Synology with 10GbE NICs installed. Actual results may vary depending on system configuration, testing methods, and other environmental variables. Check the performance page for additional details.
  2. Network adapter cards, expansion units, other PCIe add-in cards, and storage drives are sold separately. Refer to the compatibility list for compatible devices.
  3. SSD cache can be enabled by using compatible 2.5" SSDs or without occupying drive bays by installing Synology SNV3500 M.2 22110 NVMe SSDs using M2D20 or E10M20-T1 adapter cards, sold separately.
  4. Users have reported total data size reductions of more than 50% when backing up multiple systems with deduplication technology.
  5. Surveillance Station includes 2 free licenses. Connecting more cameras and devices requires additional licenses.
  • Hardware Specs
  • Software Specs

Hardware Specifications

CPU

CPU

 CPU Model Intel Xeon D-1541
CPU Architecture 64-bit
CPU Frequency 8-core 2.1 (base) / 2.7 (turbo) GHz
Hardware Encryption Engine (AES-NI)

Memory

Memory

 System Memory 16 GB DDR4 ECC UDIMM
Memory Module Pre-installed 16 GB (16 GB x 1)
Total Memory Slots 4
Maximum Memory Capacity 64 GB (16 GB x 4)
Notes
  • 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 more information on the recommended memory configurations, visit here.
  • Synology reserves the right to replace memory modules with the same or higher frequency based on supplier's product life cycle status. Rest assured that the compatibility and stability have been strictly verified with the same benchmark to ensure identical performance.

Storage

Storage

 Drive Bays 16
Maximum Drive Bays with Expansion Unit 40 (RX1217/RX1217RP x 2)
Compatible Drive Type* (See all supported drives)
  • 3.5" SATA HDD
  • 2.5" SATA SSD
Maximum Single Volume Size*
  • 200 TB (32 GB RAM required, for RAID 5 or RAID 6 groups only)
  • 108 TB
Hot Swappable Drive
Notes
  • Storage Pool and volume creation require all drives to be listed as compatible on the device model's compatibility list.
  • "Compatible drive type" indicates drives that have been tested to be compatible with Synology products. This term does not indicate the maximum connection speed of each drive bay.
  • Each internal volume (may consist of multiple drives) is expandable up to 108 TB (with memory less than 32 GB) or 200 TB (with memory equal to or greater than 32 GB).

External Ports

External Ports

 RJ-45 1GbE LAN Port 4 (with Link Aggregation / Failover support)
RJ-45 10GbE LAN Port 2 (with Link Aggregation / Failover support)
USB 3.2 Gen 1 Port* 2
Expansion Port 2
Notes The USB 3.0 standard was renamed to USB 3.2 Gen 1 by the USB Implementers Forum (USB-IF) in 2019.

PCIe

PCIe

 PCIe Expansion 2 x Gen3 x8 slots (x8 link)

File System

File System

 Internal Drives
  • Btrfs
  • EXT4
External Drives
  • Btrfs
  • EXT4
  • EXT3
  • FAT
  • NTFS
  • HFS+
  • exFAT*
Notes exFAT Access is purchased separately in Package Center.

Appearance

Appearance

 Form Factor (RU) 3U
Size (Height x Width x Depth) 132.3 mm x 482 mm x 656.5 mm
Weight 17.4 kg
Rack Installation Support* 4-post 19" rack (Synology Rail Kit - RKS1317)
Notes The rail kit is sold separately

Others

Others

 System Fan 80 mm x 80 mm x 3 pcs
Fan Speed Mode
  • Full-Speed Mode
  • Cool Mode
  • Quiet Mode
Easy Replacement System Fan
Power Recovery
Noise Level* 44.7 dB(A)
Scheduled Power On / Off
Wake on LAN / WAN
Power Supply Unit / Adapter 800 W
Redundant Power Supply
AC Input Power Voltage 100 V to 240 V AC
Power Frequency 50/60 Hz, Single Phase
Power Consumption* 145.79 W (Access)
62.68 W (HDD Hibernation)
British Thermal Unit 497.14 BTU/hr (Access)
213.74 BTU/hr (HDD Hibernation)
Notes
  • Power consumption is measured when it is fully loaded with Synology 8TB HAT5300-8T hard drive(s).
  • 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

Temperature

 Operating Temperature 0°C to 35°C (32°F to 95°F)
Storage Temperature -20°C to 60°C (-5°F to 140°F)
Relative Humidity 5% to 95% RH

Certification

Certification
  • FCC
  • CE
  • BSMI
  • VCCI
  • RCM
  • EAC
  • CCC
  • KC
  • UL

Warranty

Warranty

 5 Years
Notes The warranty period starts from the purchase date as stated on your purchase receipt. (Learn more)

Environment

Environment

 RoHS Compliant

Packaging Content

Packaging Content
  • Main Unit X 1
  • Accessory Pack X 1
  • AC Power Cord X 2
  • Quick Installation Guide X 1

Optional Accessories

Optional Accessories
Notes All memory modules will operate at the maximum frequency specified by the CPU manufacturer.

DSM Specifications

Storage Management

Storage Management

 Maximum Internal Volume Number 256
SSD Read / Write Cache (White Paper)
SSD TRIM
RAID Group
Supported RAID Type
  • 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
Volume Expansion with Larger HDDs
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10
Volume Expansion by Adding a HDD
  • RAID F1
  • JBOD
  • RAID 5
  • RAID 6
Global Hot Spare Supported RAID Type
  • RAID F1
  • RAID 1
  • RAID 5
  • RAID 6
  • RAID 10

File Services

File Services

 File Protocol CIFS/AFP/NFS/FTP/WebDAV
Maximum Concurrent CIFS/AFP/FTP Connections 4,000
Maximum Concurrent CIFS/AFP/FTP Connections (with RAM expansion) 10,000
Windows Access Control List (ACL) Integration
NFS Kerberos Authentication
Notes
  • Regarding data concerning tests with RAM expansion, all memory slots are installed with the maximum capacity of supported RAM.
  • During testing, the maximum number of SSDs supported by this model is installed in a RAID 5 configuration.
  • The testing standard was based on the maximum number of concurrent connections supported by this model. During the testing, 25% of the connections were used to transfer files concurrently. The transfer process guaranteed that the connections were not interrupted; the minimum transfer speed was not guaranteed.

Account & Shared Folder

Account & Shared Folder

 Maximum Local User Accounts 16,000
Maximum Local Groups 512
Maximum Shared Folder 512
Maximum Shared Folder Sync Tasks 32

High Availability

High Availability

 Synology High Availability

Log Center

Log Center
Syslog Events per Second 3,000

Virtualization

Virtualization

 VMware vSphere with VAAI
Windows Server 2016
Windows Server 2019
Citrix Ready
OpenStack

General Specifications

General Specifications

 Networking Protocols SMB1 (CIFS), SMB2, SMB3, NFSv3, NFSv4, NFSv4.1, NFS Kerberized sessions, iSCSI, HTTP, HTTPs, FTP, SNMP, LDAP, CalDAV
Supported Browsers
  • Google Chrome
  • Firefox
  • Microsoft Edge
  • Internet Explorer 10 onwards
  • Safari 10 onwards
  • Safari (iOS 10 onwards)
  • Google Chrome (Android 6.0 onwards)
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

Add-on Packages view the complete package list

Antivirus by McAfee (Trial)

Antivirus by McAfee (Trial)

Central Management System

Central Management System

Synology Chat

Synology Chat
Maximum Users 6,000
Notes
  • The number of concurrent HTTP connections for Synology Chat was configured to the maximum.
  • For tested models with expandable memory, the maximum amount of RAM was installed.

Document Viewer

Document Viewer

Download Station

Download Station
Maximum Concurrent Download Tasks 80

exFAT Access (Optional)

exFAT Access (Optional)

iSCSI Manager

iSCSI Manager

 Maximum iSCSI Target Number 256
Maximum iSCSI LUN 512
iSCSI LUN Clone/Snapshot, Windows ODX

Synology MailPlus / MailPlus Server

Synology MailPlus / MailPlus Server
Free Email Accounts 5 (Licenses required for additional accounts)
Maximum Number of Concurrent Users 1,100
Maximum Server Performance 4,312,000 emails per day, approx. 131GB
Notes
  • Models with more than 4 bays were installed with two SSDs for SSD cache.
  • For tested models with expandable memory, the maximum amount of RAM was installed.
  • The performance of the mail system will slightly decrease in high-availability mode due to data synchronization between the two servers.
  • Functions that were enabled in all of the tests above: anti-spam, anti-virus, DNSBL, greylist, content scan, full-text search (English only).

Media Server

Media Server
DLNA Compliance

Moments

Moments
Facial Recognition
Subject Recognition
Auto Color & Rotate
Moments Select

Snapshot Replication

Snapshot Replication
Maximum Snapshots per Shared Folder 1,024
Maximum of System Snapshots 65,536

Surveillance Station

Surveillance Station
Maximum IP cam (Licenses required) 90 (including 2 Free License) (See All Supported IP Cameras)
Total FPS (H.264) 2700 FPS @ 720p (1280x720)
2250 FPS @ 1080p (1920x1080)
1500 FPS @ 3M (2048x1536)
900 FPS @ 5M (2591x1944)
550 FPS @ 4K (3840x2160)
Total FPS (H.265) 2700 FPS @ 720p (1280x720)
2700 FPS @ 1080p (1920x1080)
2250 FPS @ 3M (2048x1536)
1500 FPS @ 5M (2591x1944)
1080 FPS @ 4K (3840x2160)
Notes
  • Surveillance Station throughput is tested with Axis network camera, using continuous recording with live view from Surveillance Station and motion detection by camera. Live view and recording are sharing the same stream from the camera.
  • The maximum channel number also includes devices installed on Virtual DSM.
  • Total FPS may be affected by other services running at the same time (e.g., archive tasks performed by Archive Vault).

Synology Drive

Synology Drive
Recommended Number of Hosted Files 5,000,000 (applies to files indexed or hosted by Synology Drive. For file access through other standard protocols, refer to the File Services section above)
Recommended Number of Concurrent Sync Clients 2,000 (the number of connections that can be maintained when the recommended number of hosted files was reached)
Notes
  • Exceeding the recommended numbers above will not block application operations, but may result in longer response time.
  • Utilizing SSD cache can significantly improve performance.
  • For tested models with expandable memory, the maximum amount of RAM was installed.
  • Btrfs file system and non-encrypted shared folders were used during the aforementioned testing.

Synology Office

Synology Office
Maximum Users 3,000
Notes
  • Multiple files were opened for testing and each file was edited by 30 users simultaneously.
  • For tested models with expandable memory, the maximum amount of RAM was installed.
  • Client performance may affect maximum simultaneous editing users. Client PCs used for testing: Intel Core i3-3220 / 8GB RAM

Video Station

Video Station

Virtual Machine Manager

Virtual Machine Manager
Recommended Virtual Machine Instances 16 (Learn more)
Recommended Virtual DSM Number (Licenses required) 16 (including 1 Free License)
Notes The specifications vary depending on system configuration and memory size.

VPN Server

VPN Server
Maximum Connections 40

Notes:

  • Model specifications are subject to change without prior notice.
  • The figures are based on Synology internal testing. Each performance test is done individually. No other services or applications are processed at the same time.
  • The actual performance may be lower than lab testing figure due to differences in server configuration, deployment, and the number of active operations.
  • If usage requirements exceed the specifications above, please contact our regional partners for professional advice.