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.
Intel® Xeon® D-1541 8-core 2.1 GHz
Built-in dual-port 10GbE
16 GB ECC DDR4 Up to 64 GB
Up to 40 drive bays with RX1217(RP)
The RS4021xs+ ensures mission-critical data is always available, enabling businesses to deliver the best results, even in the face of disaster.
Dual PSUs provide protection against a PSU failure or accidental cord removal while hot-swappable fans can be replaced without powering down the system.
Synology High Availability (SHA) pairs two identical units together creating an active-passive cluster with minute-level failover. Learn more
Btrfs prevents data corruption and reduces maintenance overheads with advanced storage technologies and optimized snapshots. Learn more
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
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
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
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
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
AES-256 encryption keeps locally-stored footage secure.
Access recordings and live streams whenever you want using a web browser, desktop client, or the DS cam mobile app.
Email, SMS, or push notifications alert you when incidents occur or predefined conditions are met.
Engineered to handle intensive 24/7 workloads, Synology drives consistently deliver top-grade performance.
The RS4021xs+ runs Synology DiskStation Manager (DSM), the web-based operating system equipped with powerful applications and services for business.
Conveniently manage your fleet of Synology NAS from a centralized console.
Instantly access your NAS files across multiple devices whenever you want, wherever you are.
Satisfy all team collaboration needs behind the safety of your own private cloud with Synology Office, Calendar, and Chat.
Run various operating systems in isolated sandboxes. Seamlessly clone, store, and migrate virtual machines.
Secure data with comprehensive built-in security tools to protect your devices against evolving threats.
Back up and synchronize data easily between public cloud accounts and your NAS.
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
SRS provides free advance replacement units as early as the next business day in selected regions, maximizing the service uptime for your mission-critical storage and ensuring your business continuity. Learn more
Hardware Specifications |
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CPU |
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CPU
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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 |
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Memory
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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 |
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Storage
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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 |
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External Ports
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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 |
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PCIe
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PCIe Expansion | 2 x Gen3 x8 slots (x8 link) |
File System |
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File System
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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. | |
Appearance |
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Appearance
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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 |
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Others
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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 |
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| 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) |
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| British Thermal Unit |
497.14 BTU/hr (Access) 213.74 BTU/hr (HDD Hibernation) |
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| Notes |
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Temperature |
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Temperature
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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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Certification
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Warranty |
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Warranty
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5 Years | |
| Notes | The warranty period starts from the purchase date as stated on your purchase receipt. (Learn more) | |
Environment |
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Environment
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RoHS Compliant | |
Packaging Content |
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Packaging Content
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Optional Accessories |
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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. | |
DSM Specifications |
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| Maximum Single Volume Size* |
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| Maximum Internal Volume Number | 256 | |
| SSD Read / Write Cache (White Paper) | ||
| 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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| 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 |
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| Maximum Local User Accounts | 16,000 | |
| Maximum Local Groups | 512 | |
| Maximum Shared Folder | 512 | |
| Maximum Shared Folder Sync Tasks | 32 | |
| Hybrid Share Folder Number | 15 | |
| Synology High Availability | ||
| Syslog Events per Second | 3,000 | |
Virtualization |
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Virtualization
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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 |
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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 |
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Antivirus by McAfee (Trial) |
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Antivirus by McAfee (Trial)
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| Maximum Users | 6,000 | |
| Maximum Number of Concurrent Users | 500 | |
| Notes | When applicable, tested systems are configured with maximum memory and set to allow the maximum number of connections. | |
Document Viewer |
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Document Viewer
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Download Station |
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Download Station
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| 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 |
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| 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) |
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| Total FPS (H.265) |
2700 FPS @ 720p (1280x720) 2700 FPS @ 1080p (1920x1080) 2250 FPS @ 3M (2048x1536) 1500 FPS @ 5M (2591x1944) 1080 FPS @ 4K (3840x2160) |
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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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| Maximum Users | 3,000 | |
| 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 | |
