Can You Mix Different Drive Sizes in RAID? The Complete Guide

Updated: 2026-04-29

Last updated March 2026 · 7 min read

You have a 4TB drive, two 8TB drives, and a 12TB drive. Can you combine them in a RAID array? The answer depends entirely on which RAID type you choose – and the difference in usable storage can be dramatic.

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The Short Answer

Yes, you can mix drive sizes in most RAID types. But traditional RAID (0, 5, 6, 10) will limit every drive to the size of the smallest one, wasting significant capacity. SHR, Unraid, and JBOD handle mixed sizes much better.

Traditional RAID with Mixed Drives

In RAID 5 with drives of 4TB + 8TB + 8TB + 12TB, the usable capacity is 3 × 4TB = 12TB. You're wasting 20TB of raw capacity. The same applies to RAID 6 (2 × 4TB = 8TB usable from 32TB raw) and RAID 0 (4 × 4TB = 16TB usable). The calculation always uses the smallest drive as the baseline.

RAID 10 pairs drives into mirrors, then stripes. With mixed sizes, each mirror pair uses the smaller drive's capacity.

SHR – The Mixed-Size Champion

Synology's SHR was designed specifically for mixed drives. It creates layered RAID volumes across capacity tiers. With 4TB + 8TB + 8TB + 12TB in SHR-1, you get approximately 20TB usable instead of 12TB in RAID 5. That is 67% more storage from the same hardware.

Unraid – Individual Drive Flexibility

Unraid stores files on individual drives (no striping), using the largest drive as parity. With 4TB + 8TB + 8TB + 12TB, your parity drive is 12TB and your data drives give you 4 + 8 + 8 = 20TB usable. Every drive can be a different size – the only rule is that no data drive can be larger than the parity drive.

ZFS RAIDZ – Same Problem as Traditional RAID

ZFS RAIDZ behaves like traditional RAID regarding mixed sizes – all drives in a vdev are limited to the smallest drive's capacity. ZFS is designed around uniform vdevs. If you have mixed drives, you'd create multiple smaller vdevs or accept the wasted space.

JBOD – Maximum Capacity, Zero Protection

JBOD simply concatenates all drives. 4 + 8 + 8 + 12 = 32TB usable. But there is zero redundancy. If any drive fails, you lose the data on that drive.

Real-World Example: 4TB + 8TB + 8TB + 12TB

Here's what each RAID type gives you with these four drives (32TB raw):

JBOD gives 32TB with no protection. Unraid and SHR-1 give around 20TB with single-drive protection. RAID 5 gives only 12TB with single-drive protection. RAID 6 gives 8TB with double protection. RAID 10 gives roughly 12TB.

The difference between SHR/Unraid (20TB) and RAID 5 (12TB) is 8TB of usable storage – essentially a free drive's worth.