4-Bay or 6-Bay NAS Devices? Compared by Specs
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This comparison covers 4-Bay vs 6-Bay network attached storage options from Synology. Both units are diskless, meaning you supply your own drives. They share the Synology brand and DSM operating system for management. The main difference lies in capacity and form factor. One unit offers four bays in a rackmount design. The other provides six bays for 2.5-inch drives in a compact desktop chassis. You must choose based on your drive type and space constraints.
Key differences
| Aspect | Synology 4-Bay Rackmount Expansion Unit | Synology 6-Bay 2.5 Inch NAS DS620slim |
|---|---|---|
| Number of Bays | 4-Bay | 6-Bay |
| Drive Form Factor | Not listed | 2.5 Inch |
| RAM Capacity | Not listed | 2GB DDR3L, expandable to 6GB |
| Form Factor | Rackmount (12-inch depth) | Desktop (Mini-sized) |
| Video Transcoding | Not listed | Dual-channel H.265/H.264 4K |
Which one should you choose?
Choose Synology 4-Bay Rackmount Expansion Unit if
- You need a rackmount solution for a 2-post or wall mount rack
- You prefer a deeper unit designed for server environments
- You require a diskless expansion unit for existing storage
Choose Synology 6-Bay 2.5 Inch NAS DS620slim if
- You want to use small 2.5-inch SSDs or HDDs
- You need expandable RAM for better performance
- You require 4K video transcoding capabilities
Verdict: Choose the 4-Bay unit if you need rackmount flexibility and a deeper chassis for server setups. Select the 6-Bay unit if you prefer compact desktop space, 2.5-inch drives, and enhanced RAM and transcoding features. Your decision depends entirely on your physical space and drive format preferences.
4-Bay vs 6-Bay NAS Specs
Number of Bays
The Synology RX418 provides four drive bays for storage expansion. This unit is designed as a diskless expansion unit, meaning you must supply your own hard drives. In contrast, the Synology DS620slim offers six drive bays. This higher bay count allows for greater storage capacity and more RAID configuration options. If you need maximum space in a single chassis, the six-bay model provides a clear advantage. The four-bay unit is better if you prefer a smaller footprint or are expanding an existing system. The difference in bay count is the most significant physical distinction between these two devices.
Form Factor
Form factor differences are stark. The RX418 is a rackmount expansion unit measuring 44 mm in height, 480 mm in width, and 325 mm in depth. It weighs 9.44 pounds. This size is suited for 2-post racks or wall mounts. The DS620slim is a desktop unit with a compact design. It measures 5.94 inches in width, 4.76 inches in height, and 6.89 inches in depth. It weighs only 3.09 pounds. The RX418 is significantly larger and heavier. The DS620slim is much more portable and fits easily on a desk. Your choice depends on whether you need rackmount infrastructure or desktop convenience.
RAM Capacity
Memory specifications vary between the two units. The DS620slim comes with 2GB of DDR3L memory. This memory is expandable up to 6GB, allowing for better performance with heavy workloads. The RX418 data does not list specific RAM capacity. As an expansion unit, its memory requirements may differ from a standalone NAS. If you need expandable RAM for demanding tasks, the DS620slim offers a documented upgrade path. The RX418 is managed via DSM but lacks explicit RAM details in the provided data. For memory flexibility, the six-bay model has the edge.
Drive Compatibility
Drive compatibility is a key differentiator. The DS620slim supports 2.5-inch HDDs and SSDs. This allows for smaller, potentially faster storage options in a dense package. The RX418 is a 4-bay unit, but the data does not specify drive size. Typically, expansion units like the RX418 support 3.5-inch drives, but this is not explicitly stated in the provided specs. The DS620slim explicitly supports 2.5-inch drives. If you prefer 2.5-inch drives for their size or speed, the DS620slim is the clear choice. The RX418 is diskless, requiring you to provide compatible drives for its bays.
Video Transcoding
Multimedia capabilities differ significantly. The DS620slim features dual-channel H.265/H.264 4K video transcoding. This allows it to handle 4K video streams on the fly, which is useful for media servers. The RX418 data does not mention video transcoding capabilities. As an expansion unit, its primary role is storage expansion rather than media processing. If you plan to use this device for media streaming or transcoding, the DS620slim offers this specific hardware feature. The RX418 is better suited for pure storage expansion. For multimedia tasks, the six-bay model has the advantage.
Choose Your Synology NAS Model
Users needing extra rackmount storage
The Synology RX418 is a 4-bay expansion unit designed for seamless integration. It measures 1.73 inches in height and fits 2-post racks. You get online volume expansion and deep sleep mode for energy savings. It manages easily via DSM, making it ideal for adding capacity to existing setups without replacing your main server.
Users wanting compact 2.5-inch drive support
The Synology DS620slim supports six 2.5-inch drives in a small white chassis. It weighs only 3.09 pounds and offers 2GB of expandable RAM. You get over 220 MB/s read speeds and 4K video transcoding. This unit provides better RAID flexibility for SSDs and HDDs, maximizing productivity in a minimal footprint.
Users requiring high snapshot capabilities
The DS620slim uses the Advanced Btrfs file system to support up to 65,000 system-wide snapshots. You can also create 1,024 snapshots per shared folder. This data protection level, combined with its 6-bay capacity and 108 TB maximum volume size, makes it suitable for users prioritizing data integrity and recovery options.
Quick picks
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | Synology 4-Bay Rackmount Expansion Unit | expanding existing Synology NAS storage | Check price of Synology 4-Bay Rackmount Expansion Unit on Amazon |
| 2 | Synology 6-Bay 2.5 Inch NAS DS620slim | compact 2.5-inch drive storage | Check price of Synology 6-Bay 2.5 Inch NAS DS620slim on Amazon |
The products compared
Synology 4-Bay Rackmount Expansion Unit
Best for: expanding existing Synology NAS storage
- Number of Bays
- 4-Bay (what this guide is about)
- Drive Bays
- 4-Bay
- Included Storage
- Diskless
- Dimensions
- 17 × 11.4 × 1.73 inches
- Weight
- 9.44 pounds
View on Amazon: Synology 4-Bay Rackmount Expansion Unit Affiliate link
This Synology RX418 is a 4-bay diskless expansion unit designed to add storage to an existing NAS. It measures 17 x 11.4 x 1.73 inches and weighs 9.44 pounds. You can manage it via Synology DSM. The unit supports online volume expansion and plug-and-play setup. It fits 2-post racks. It is ideal for users needing more space without buying a new main unit.
Pros
- 4-bay diskless design for seamless upgrade
- Online volume expansion capability
- Compact 17-inch depth fits 2-post racks
- Managed through Synology DSM software
Cons
- Sold diskless with no included storage
- Requires a host NAS to function
- No internal processing power for standalone use
Good fit if
- You need to expand an existing Synology NAS
- You want a diskless unit for cost efficiency
- You have a 2-post rack available
Skip if
- You need a standalone NAS server
- You want pre-installed hard drives
- You require a 6-bay configuration
Verdict: Synology 4-Bay Diskless Expansion Unit is a practical add-on for users who already own a Synology NAS and need more drive slots. It is not a standalone solution.
Synology 6-Bay 2.5 Inch NAS DS620slim
Best for: compact 2.5-inch drive storage
- Number of Bays
- 6-Bay (what this guide is about)
- Drive Bays
- 6 Bay
- RAM Capacity
- 2GB DDR3L
- Included Storage
- Diskless
- Form Factor
- 2.5 Inch
- Dimensions
- 6.89 × 5.94 × 4.76 inches
View on Amazon: Synology 6-Bay 2.5 Inch NAS DS620slim Affiliate link
The Synology DS620slim is a 6-bay NAS designed for 2.5-inch drives. It offers RAID flexibility for HDDs and SSDs. The unit includes 2GB of DDR3L memory, expandable to 6GB. It supports dual-channel H.265/H.264 4K video transcoding. The Advanced Btrfs file system allows for extensive snapshot capabilities. This device suits users needing high capacity in a compact form factor.
Pros
- Six drive bays for 2.5-inch HDDs and SSDs
- Memory expands from 2GB to 6GB
- Supports 4K video transcoding
- Advanced Btrfs file system with 65,000 snapshots
Cons
- Limited to 2.5-inch drive form factor
- Diskless unit requires separate drive purchase
- No mention of included software or apps
Good fit if
- You need high storage capacity in a small footprint
- You prefer 2.5-inch drives for lower power use
- You want extensive snapshot features for data protection
Skip if
- You require 3.5-inch drive bays
- You need pre-installed drives
- You want a device with a built-in display
Verdict: Synology DS620slim 6-Bay NAS fits users who prioritize compact size and 2.5-inch drive compatibility for high-capacity storage.
Specifications side by side
| Spec | Synology 4-Bay Rackmount Expansion Unit | Synology 6-Bay 2.5 Inch NAS DS620slim |
|---|---|---|
| Drive Bays | 4-Bay | 6 Bay |
| RAM Capacity | not stated | 2GB DDR3L |
| Included Storage | Diskless | Diskless |
| Form Factor | not stated | 2.5 Inch |
| Number of Bays | 4-Bay | 6-Bay |
| Dimensions | 17 × 11.4 × 1.73 inches | 6.89 × 5.94 × 4.76 inches |
| Weight | 9.44 pounds | 3.09 pounds |
| Size | 44 mm x 480 mm x 325 mm | 6-bay; 2GB DDR3L |
| Color | black | white |
| Model | RX418 | DS620slim |
Frequently asked questions
Can I use these units without drives installed?
Yes, both the Synology RX418 and DS620slim are diskless. You must supply your own hard drives to populate the bays. This allows you to choose specific drive types and capacities that fit your storage needs. The units provide the chassis and connectivity but do not include internal storage media.
What is the physical size difference between the 4-bay and 6-bay models?
The RX418 is a rackmount expansion unit measuring 17 inches in length and 1.73 inches in height. It is designed for 2-post racks. The DS620slim is a compact desktop unit measuring 6.89 inches in length and 4.76 inches in height. It is significantly smaller in footprint.
Does the 6-bay model support standard 3.5-inch hard drives?
No, the Synology DS620slim is designed for 2.5-inch drives. Its form factor is listed specifically as 2.5 Inch. This makes it suitable for compact high-capacity storage using smaller drives. It does not accommodate standard 3.5-inch desktop hard drives found in many other NAS enclosures.
Are both devices compatible with the same operating system?
Yes, both units run the Synology DSM operating system. This ensures a consistent management interface regardless of the chassis size. You can manage storage, applications, and user permissions using the same software environment on either the 4-bay expansion unit or the 6-bay compact NAS.
How much weight do these NAS units add to a setup?
The RX418 weighs 9.44 pounds due to its larger chassis and rackmount design. The DS620slim is much lighter at 3.09 pounds. This weight difference reflects their different build purposes. The heavier unit is built for rack stability, while the lighter one is for desktop placement.
Can the 4-bay unit expand existing storage capacity?
Yes, the RX418 is designed as an expansion unit for existing Synology NAS devices. It allows for online volume expansion, meaning you can add storage without downtime. It is not a standalone solution but works alongside your primary NAS to increase total available drive slots.