Synology RAID / SHR Capacity Calculator
Estimate your usable storage for Synology RAID types including SHR, SHR-2, RAID 0, RAID 1, RAID 5, RAID 6, RAID 10, JBOD, and Basic.
What this RAID Synology calculator helps you answer
If you're shopping for a Synology NAS, upgrading old disks, or deciding between SHR and RAID 5, this calculator helps you quickly estimate usable capacity, protection overhead, and failure tolerance.
The key thing many people miss is that raw capacity (sum of all drives) is never the same as usable capacity. Redundancy and RAID structure always consume part of your disk pool. With mixed-size drives, some RAID levels also leave extra space unused.
RAID and SHR in plain English
SHR (Synology Hybrid RAID)
SHR is Synology’s flexible RAID system. It is designed to make better use of mixed disk sizes than traditional RAID in many practical setups. It is often the best default for home and small office deployments.
- SHR: 1-disk fault tolerance
- SHR-2: 2-disk fault tolerance
Traditional RAID levels
- RAID 0: Max capacity and speed, no redundancy
- RAID 1: Mirroring, high protection, low efficiency
- RAID 5: Single parity, good balance of capacity and protection
- RAID 6: Double parity, stronger protection for larger arrays
- RAID 10: Mirrored pairs with striping, strong performance and resiliency
- JBOD / Basic: No true RAID redundancy
How this calculator estimates capacity
The calculator uses practical rules for each RAID type. For classic RAID with mixed drives (RAID 0/5/6/10), it assumes usable calculations are constrained by the smallest drive in the set. For SHR and SHR-2, it uses an estimate based on reserved protection equivalent to one or two largest-disk chunks.
Because Synology DSM also reserves space for metadata, filesystems, and system partitions, real-world usable space shown inside DSM will usually be a bit lower than this estimate.
Example planning scenarios
Scenario 1: Four 8 TB drives in SHR
Raw is 32 TB. SHR typically gives around 24 TB usable, with ~8 TB reserved for protection. This is why SHR is so popular: straightforward capacity with 1-drive redundancy.
Scenario 2: Mixed drives (12, 12, 8, 8) in RAID 5
RAID 5 is constrained by the smallest size for stripe parity math, so much of the extra 12 TB capacity can be stranded. You get consistency, but lower utilization than many users expect.
Scenario 3: Large media archive in SHR-2
If uptime and data durability matter more than absolute capacity, SHR-2 (or RAID 6) can be a better fit. You lose more space, but survive two drive failures.
Choosing the right option for your Synology NAS
- Home users: SHR is usually the easiest and most flexible.
- Business with critical data: Consider SHR-2 or RAID 6.
- Performance-heavy workloads: RAID 10 can make sense if you can afford lower capacity efficiency.
- Never use RAID as backup: RAID protects availability, not against deletion, ransomware, or fire.
Common mistakes this tool helps avoid
- Buying mismatched disks without understanding wasted space.
- Assuming “4 × 10 TB = 40 TB usable.”
- Choosing RAID 0 for important files.
- Skipping a backup strategy because “RAID is enough.”
Final notes
Use this RAID Synology calculator early in your NAS planning process. It will help you compare tradeoffs before you buy disks, and avoid expensive upgrades later. Then validate your final numbers using Synology’s official documentation and your target DSM version.