RackStation® RS4021xs+ | Synology Inc.

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 throughput. 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.

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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

Customized to your business

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

Double bandwidth

Upgrade network speeds by double or more with Synology's range of 10Gbe NICs.

SSD cache

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 RX1217RP/RX1217 expansion units.

The ultimate backup solutions — license-free

Keep disaster at bay

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. Deduplication, 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

Backup your entire IT infrastructure

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 cameras 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.

HDD

Enterprise Series 3.5" SATA

SSD

Enterprise Series 2.5" SATA

Enterprise Series M.2 NVMe

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.

Learn more

Synology Drive

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

Learn more

Collaboration Suite

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

Learn more

Virtual Machine Manager

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

Learn more

Security

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

Learn more

Public Cloud Integration

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

Learn more

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

Hardware Overview

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
CPU
CPU	CPU Model	Intel Xeon D-1541
	CPU Quantity	1
	CPU Core	8
	CPU Architecture	64-bit
	CPU Frequency	2.1 (base) / 2.7 (turbo) GHz
	Hardware Encryption Engine
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 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
Storage	Drive Bays	16
	Maximum Drive Bays with Expansion Unit	40 (RX1217 x 2)
	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.
External Ports
External Ports	RJ-45 1GbE LAN Port	4
	RJ-45 10GbE LAN Port	2
	USB 3.2 Gen 1 Port	2
	Expansion Port	2
	Expansion Port Type	Infiniband
PCIe
PCIe	PCIe Expansion	2 x Gen3 x8 slots (x8 link)
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 watts 550 watts*
	Redundant Power Supply
	AC Input Power Voltage	100 V to 240 V AC
	Power Frequency	50/60 Hz, Single Phase
	Power Consumption*	145.79 watts (Access) 62.68 watts (HDD Hibernation)
	British Thermal Unit	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. 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
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 BIS 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	DDR4 ECC UDIMM: D4EC-2666-16G Expansion Units: RX1217/RX1217RP Enterprise Series 3.5" SATA HDD: HAT5300 Series Enterprise Series 2.5" SATA SSD: SAT5200 Series M.2 SSD & 10GbE Combo Adapter Card: E10M20-T1 M.2 SSD Adapter Card: M2D20 25GbE Network Interface Card: E25G30-F2 10GbE Network Interface Card: E10G30-F2/E10G30-T2/E10G18-T1 Rail Kit Sliding: RKS-02
	Notes	All memory modules will operate at the maximum frequency specified by the CPU manufacturer.

DSM Specifications
Storage Management
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
	Maximum Internal Volume Number	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 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	Volumes over 108 TB require 32 GB of memory or more. 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. When Peta Volume is enabled, validated services and packages are required. Please refer to this article for more information on limitations.
File System
File System	Internal Drives	Btrfs ext4
	External Drives	Btrfs ext4 ext3 FAT32 NTFS HFS+ exFAT
File Services
File Services	File Protocol	SMB AFP NFS FTP WebDAV Rsync
	Maximum Number of SMB Connections (FSCT-Based)	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. The testing standard was based on client computers running Windows Server 2022 and Microsoft File Server Capacity Tool (FSCT).
Account & Shared Folder
Account & Shared Folder	Maximum Local User Accounts	5,120
	Maximum Local Groups	512
	Maximum Shared Folder	512
	Maximum Shared Folder Sync Tasks	32
Hybrid Share
Hybrid Share	Hybrid Share Folder Number	15
Hyper Backup
Hyper Backup	Folder and Package Backup
	Entire System Backup
	Notes	Full-system backup requires DSM 7.2 or later.
High Availability
High Availability	Synology High Availability
Log Center
Log Center
	Syslog Events per Second	3,000
Virtualization
Virtualization	VMware ESXi 6.5 and VAAI
	Windows Server 2016
	Windows Server 2019
	Windows Server 2022
	Citrix Ready
	OpenStack
General Specifications
General Specifications	Supported Protocols	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
	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
Central Management System
Central Management System
Synology Chat
Synology Chat
	Suggested Users	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.
Download Station
Download Station
	Maximum Concurrent Download Tasks	80
SAN Manager
SAN Manager
	Maximum iSCSI Target Number	128
	Maximum LUN	256
	LUN Clone/Snapshot, Windows ODX
Synology MailPlus / MailPlus Server
Synology MailPlus / MailPlus Server
	Free Email Accounts	5 (Additional accounts require purchase of licenses)
	Suggested Users	3,200
	Notes	Suggested users is derived from testing in an environment with 20% heavy users (each with 20,000 pre-populated emails and receiving 240 emails per day) and 80% light users (each receiving an average of 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
Media Server
	DLNA Compliance
Synology Photos
Synology Photos
	Facial Recognition
	Object Recognition
Snapshot Replication
Snapshot Replication
	Maximum Snapshots per Shared Folder	512
	Maximum of System Snapshots	16,384
Surveillance Station
Surveillance Station
	Default Licenses	2 (Additional cameras require purchase of licenses)
	Suggested Maximum IP Cameras and Total FPS (H.264)	1080p: 280 channels, 2800 FPS 3M: 200 channels, 2000 FPS 5M: 120 channels, 1200 FPS 4K: 85 channels, 850 FPS
	Suggested Maximum IP Cameras and Total FPS (H.265)	1080p: 285 channels, 8550 FPS 3M: 280 channels, 2800 FPS 5M: 200 channels, 2000 FPS 4K: 120 channels, 1200 FPS
	Notes	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 streams that can be viewed simultaneously is twice the suggested maximum number of cameras. For example, if the suggested maximum number of cameras for a model is 10 under H.264, 1080p, the model can support up to 20 streams of the same specification at the same time.
Synology Drive
Synology Drive
	Suggested Users	2,700
	Maximum Number of Hosted Files	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.
Synology Office
Synology Office
	Suggested Users	2,700
	Notes	Suggested users is derived from testing in an environment with 60% idle users (each logging in and viewing documents) and 40% active users (each executing random actions at intervals of 20 to 40 seconds) operating within documents, each document having 30 users. 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
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	32

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.