RackStation RS4021xs+
Enterprise NAS with built-in service continuity engineered for data-intensive applications.
Securing your business assets
The 16-bay RS4021xs+ provides solid data security and lightening-fast performance with over 234K 4K random read IOPS and 6,258 MB/s sequential read throughput1. Together with its 8-core processor, ECC memory, advanced snapshot technology, and built-in 10GbE connectivity, the RS4021xs+ can support large multi-user environments while handling data-intensive workloads.
Compute
Intel® Xeon® D-1541 8-core 2.1 GHz
Networking
Built-in dual-port 10GbE
Memory
16 GB ECC DDR4 Up to 64 GB
Scalability
Up to 40 drive bays with RX1217RP/RX1217
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
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
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
Storage for virtualization
Synology iSCSI storage supports mainstream virtualization solutions with an easy management interface to enhance usability. VMware vSphere 6.5 and VAAI integration helps offload storage operations. Windows Offloaded Data Transfer (ODX) speeds up data transfer. OpenStack Cinder support turns your Synology NAS into a block-based storage component. Additionally, Synology Storage Console enables even more simplified storage provisioning and management options in VMware and Windows environments. Learn more
All-in-one surveillance solution
Synology Surveillance Station transforms the RS4021xs+ into a feature-packed Network Video Recorder solution. Support for up to 90 IP cameras5 and video analytics such as motion detection, no idle zone, foreign object detection, and anomaly detection cater to the most common surveillance scenarios. Learn more
Secure and private
AES-256 encryption keeps locally-stored footage secure.
Access from anywhere, anytime
Access recordings and live streams whenever you want using a web browser, desktop client, or the DS cam mobile app.
Real-time alerts
Email, SMS, or push notifications alert you when incidents occur or predefined conditions are met.
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.
Synology Drive
Instantly access your NAS files across multiple devices whenever you want, wherever you are.
Collaboration Suite
Satisfy all team collaboration needs behind the safety of your own private cloud with Synology Office, Calendar, and Chat.
Virtual Machine Manager
Run various operating systems in isolated sandboxes. Seamlessly clone, store, and migrate virtual machines.
Security
Shield your Synology NAS from the most sophisticated threats with industry-leading security solutions.
Public Cloud Integration
Back up and synchronize data easily between public cloud accounts and your NAS.
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+
- 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:
- 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.
- Network adapter cards, expansion units, other PCIe add-in cards, and storage drives are sold separately. Refer to the compatibility list for compatible devices.
- 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.
- Users have reported total data size reductions of more than 50% when backing up multiple systems with deduplication technology.
- Surveillance Station includes 2 free licenses. Connecting more cameras and devices requires additional licenses.
Hardware Specifications | ||
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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 | ||
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 |
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Storage | Drive Bays | 16 |
Maximum Drive Bays with Expansion Unit | 40 (RX1217/RX1217RP x 2) | |
Compatible Drive Type* (See all supported drives) |
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Hot Swappable Drive* | ||
Notes |
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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 Expansion | 2 x Gen3 x8 slots (x8 link) |
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 | System Fan | 80 mm x 80 mm x 3 pcs |
Fan Speed Mode |
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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 |
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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 |
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Warranty | 5 Years | |
Notes | The warranty period starts from the purchase date as stated on your purchase receipt. (Learn more) | |
Environment | RoHS Compliant | |
Packaging Content |
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Optional Accessories |
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Notes | All memory modules will operate at the maximum frequency specified by the CPU manufacturer. |
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.
DSM Specifications | ||
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Maximum Single Volume Size |
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Maximum Internal Volume Number | 256 | |
SSD Read/Write Cache (Determining cache size) | ||
SSD TRIM | ||
RAID Group | ||
Supported RAID Type |
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RAID Migration |
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Volume Expansion with Larger HDDs |
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Volume Expansion by Adding a HDD |
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Global Hot Spare Supported RAID Type |
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Notes |
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Internal Drives |
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External Drives |
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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. | |
File Protocol |
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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 |
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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 | |
Folder and Package Backup | ||
Entire System Backup | ||
Notes | Full-system backup requires DSM 7.2 or later. | |
Synology High Availability | ||
Syslog Events per Second | 3,000 | |
Virtualization | VMware ESXi 6.5 and VAAI | |
Windows Server 2016 | ||
Windows Server 2019 | ||
Windows Server 2022 | ||
Citrix Ready | ||
OpenStack | ||
Supported Protocols | SMB1 (CIFS), SMB2, SMB3, NFSv3, NFSv4, NFSv4.1, NFS Kerberized sessions, iSCSI, Fibre Channel, HTTP, HTTPs, FTP, SNMP, LDAP, CalDAV | |
Supported Browsers |
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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. | |
Add-on Packages view the complete package list | ||
Antivirus by McAfee (Trial) | ||
Suggested Maximum Users | 6,000 | |
Suggested Concurrent Users | 500 | |
Notes | When applicable, systems are tested configured with maximum memory and set to allow the maximum number of connections. | |
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 (Additional accounts require purchase of licenses) | |
Suggested Maximum Users | 10,000 | |
Suggested Concurrent Users | 2,000 | |
Maximum Server Performance | 4,312,000 emails per day, approx. 131GB | |
Notes |
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DLNA Compliance | ||
Facial Recognition | ||
Object Recognition | ||
Maximum Snapshots per Shared Folder | 1,024 | |
Maximum of System Snapshots | 65,536 | |
Default Licenses | 2 (Additional cameras require purchase of licenses) | |
Suggested Maximum IP Cameras and Total FPS (H.264) |
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Suggested Maximum IP Cameras and Total FPS (H.265) |
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Notes |
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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 |
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Suggested Maximum Users | 12,500 | |
Suggested Concurrent Users | 5,000 | |
Notes |
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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:
- 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.