RackStation RS4021xs+

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

Compute

Compute

Intel® Xeon® D-1541 8-core 2.1 GHz

Networking

Networking

Built-in dual-port 10GbE

Memory

Memory

16 GB ECC DDR4 Up to 64 GB

Scalability

Scalability

Up to 40 drive bays with RX1217(RP)

Engineered for service continuity

The RS4021xs+ ensures mission-critical data is always available, enabling businesses to deliver the best results, even in the face of disaster.

Redundant power

Dual PSUs provide protection against a PSU failure or accidental cord removal while hot-swappable fans can be replaced without powering down the system.

Maximize service availability

Synology High Availability (SHA) pairs two identical units together creating an active-passive cluster with minute-level failover. Learn more

Next-generation file system

Btrfs prevents data corruption and reduces maintenance overheads with advanced storage technologies and optimized snapshots. Learn more

Engineered for service continuity

Customize to your business

The RS4021xs+ includes two PCIe slots for performance, networking, and storage upgrades enabling it to adapt to any business environment2.

Double bandwidth

Upgrade network bandwidth in minutes by 2x or more with Synology’s range of 10GbE NICs.

SSD cache3

Boost read/write IOPS by up to 16 times by enabling SSD cache with our Synology M.2 NVMe adapter cards and SNV3500 SSDs, or by installing one or more 2.5” SAT5200 SSDs.

Storage expansion

Quickly and easily scale up to 40 drives with two RX1217(RP) expansion units.

Double bandwidth
SSD cache<sup>3</sup>
Storage expansion

The ultimate backup solutions — license-free

Hyper Backup

A comprehensive backup and recovery solution for securing data stored on Synology servers. Backup data locally, to another Synology device, rsync server, or cloud-based storage such as Google Drive, Dropbox, S3-compatible destinations, and Synology C2. Deduplication4, integrity checks, and incremental transfer technology reduce bandwidth and storage used. Learn more

Snapshot Replication

Easily schedule flexible point-in-time backups of shared folders and iSCSI LUNs with an RPO as low as 5 minutes and recovery in seconds. Set up replication and failover to other Synology storage systems for fast RTOs and minimal service disruption. Learn more

Keep disaster at bay

Active Backup Suite

Enables administrators to easily backup the entire IT infrastructure to their NAS, including Windows & Linux workstations and servers, file servers, VMware and Hyper-V virtual machines, and Microsoft 365 and Google Workspace accounts. Backups benefit from deduplication, multiversioning, and optimizations to reduce bandwidth and storage used. Learn more

Backup your entire IT infrastructure
vmware
windows2016
citrix
openstack

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.

5-year warranty

5-year warranty

At Synology, we are committed to product innovation and quality. The RS4021xs+ is backed by a 5-year limited warranty that includes technical support and hardware replacement services to maximize your return on investment. Learn more

RackStation RS4021xs+

product RS4021xsplus front view photo
product RS4021xsplus back view photo
  • 1Power button and indicator
  • 2Alert Off Button
  • 3Drive tray
  • 4Drive status indicator
  • 5PSU fan
  • 6Power Port
  • 7PSU Indicators & Alert Off Buttons
  • 8Console port
  • 91GbE/10GbE RJ-45 Ports
  • 10USB 3.2 Ports
  • 11Expansion port
  • 12PCIe expansion slot
  • 13Reset 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 Specifications
CPU
CPU
CPU Model Intel Xeon D-1541
CPU Quantity 1
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
  • 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.
  • 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 about the recommended memory configurations, please check the Hardware Installation Guide of your Synology product.
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
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.
  • "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.
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 can be installed for free from Package Center in DSM 7.0. In DSM 6.2 or earlier versions, exFAT Access needs to be purchased 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 - RKS-02)
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
550 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 supply specifications may differ based on the hardware revision of the device. For more information, refer to the Product Change Notice.
  • 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
Maximum Single Volume Size*
  • 1 PB (64GB RAM required)
  • 200 TB (32 GB memory required)
  • 108 TB
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
Notes
  • 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.
  • On Peta Volume enabled volumes, Snapshot Replication, SSD caching, shared folder encryption, and compression will not be available. Please refer to this article for more information on limitations.
  • Actual maximum storage pool and volume sizes depend on drive sizes used, the number of drive bays available, and the RAID configuration.
  • 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).
File Protocol SMB/AFP/NFS/FTP/WebDAV
Maximum Concurrent SMB/AFP/FTP Connections 4,000
Maximum Concurrent SMB/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.
Maximum Local User Accounts 16,000
Maximum Local Groups 512
Maximum Shared Folder 512
Maximum Shared Folder Sync Tasks 32
Maximum Hybrid Share Folders 15
Notes For more details about the maximum number of Hybrid Share folders, check this article.
Synology High Availability
Syslog Events per Second 3,000
Virtualization
Virtualization
VMware vSphere with VAAI
Windows Server 2016
Windows Server 2019
Citrix Ready
OpenStack
Networking Protocols SMB1 (CIFS), SMB2, SMB3, NFSv3, NFSv4, NFSv4.1, NFS Kerberized sessions, iSCSI, Fibre Channel, HTTP, HTTPs, FTP, SNMP, LDAP, CalDAV
Supported Browsers
  • Google Chrome
  • Firefox
  • Microsoft 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
Notes For an updated list of supported browser versions, check the DSM Technical Specifications.
Antivirus by McAfee (Trial)
Antivirus by McAfee (Trial)
Maximum Users 6,000
Maximum Number of Concurrent Users 500
Notes When applicable, systems are tested configured with maximum memory and set to allow the maximum number of connections.
Document Viewer
Document Viewer
Download Station
Download Station
Maximum Concurrent Download Tasks 80
Maximum iSCSI Target Number 256
Maximum LUN 512
LUN Clone/Snapshot, Windows ODX
Notes iSCSI Manager has been renamed to SAN Manager in DSM 7.0.
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).
DLNA Compliance
Facial Recognition
Maximum Snapshots per Shared Folder 1,024
Maximum of System Snapshots 65,536
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
  • Maximum IP cameras and FPS figures are tested with the device fully populated with drives and under a continuous recording setup.
  • Actual system capabilities may differ depending on system configuration, drive performance, number of features enabled, and if additional workloads are present.
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)
Recommended Number of Hosted Files 50,000,000 (applies to files indexed or hosted by Synology Drive. For file access through other standard protocols, refer to the File Services section above)
Notes
  • 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.
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
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.
Maximum Connections 60

Notes:

  1. Model specifications are subject to change without prior notice.
  2. 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.
  3. The actual performance may be lower than lab testing figure due to differences in server configuration, deployment, and the number of active operations.
  4. If usage requirements exceed the specifications above, please contact our regional partners for professional advice.