Can I Mix Different Size Hard Drives in a NAS?
As an Amazon Associate we earn from qualifying purchases. Prices and availability come from Amazon.com as of the last update and may change.
Yes, in most cases, but the array type decides how much of each drive you get. Classic RAID and a ZFS vdev count every drive as the smallest one, so extra space on larger drives sits unused. Synology SHR, TerraMaster TRAID and Unraid are built to use mixed sizes, each with its own rule. Sizes can differ, but some things must still match, such as drive type on Synology.
Check your situation
Work it out for your hardware
Synology DS923+: 4 bays, drives up to 24TB each, from Synology DS923+ datasheet. Drive compatibility for this model.
Path 1: swap drives one at a time
Space first rises at swap 2. The swaps before it gain nothing you can use. Each swap is one rebuild of a 8TB array member: 11.1 hours at 200MB a second, 22.2 hours at 100MB a second.
| Drives swapped | Usable space | Gained | Rebuild time so far |
|---|---|---|---|
| 1 of 4 | 24TB | nothing yet | 11.1 hours to 22.2 hours |
| 2 of 4 | 32TB | +8TB | 22.2 hours to 44.4 hours |
| 3 of 4 | 40TB | +16TB | 33.3 hours to 2.8 days |
| 4 of 4 | 48TB | +24TB | 44.4 hours to 3.7 days |
The two rates are yours: read them from your NAS during a rebuild or a scrub. A system that rebuilds only the used space finishes sooner. The last step, expanding onto the new space, takes extra time this tool cannot estimate.
- Synology supports replacing drives to expand SHR, SHR-2, RAID 1, RAID 5, RAID 6, RAID 10 and RAID F1 pools.
- Replace the smallest drive first. When every drive is the same size, at least two have to be replaced with larger ones before the pool can grow.
Path 2: add drives to empty bays
All 4 bays are in use, so there is nowhere to add a drive.
Path 3: back up, start again with 4 x 16TB
A new array of 4 x 16TB in SHR (Synology Hybrid RAID) holds 48TB, the same as the end of path 1, reached in one build instead of 4 rebuilds. It needs a complete copy of your data somewhere else first, because creating the new array erases the drives. At today's cheapest 16TB drive, 4 drives cost $2,357.80.
16TB drives that fit, by price
New 3.5-inch SATA drives rated for NAS or enterprise use whose maker confirms CMR recording, no larger than this model's 24TB per-bay limit. Prices are live from Amazon.com. As an Amazon Associate the site earns from qualifying purchases.
The rules this tool applies, with their sources, are on its own page: NAS Upgrade Advisor.
Safe steps
These actions can lose data. Do none of them until a copy exists elsewhere:
- QNAP says to back up your important data before setting up or changing a RAID array. It warns that initialization erases all data on the disks.
- JBOD and RAID 0 use every drive in full but have no redundancy. Synology says that if one drive in RAID 0 fails, all data in the array is lost.
- Adding drives to a Synology pool that is not in Healthy status. Synology says the pool must be Healthy first.
- QNAP says mixed drives can make rebuilds longer and raise the risk of errors.
- TerraMaster says TRAID cannot be converted to a traditional array type unless you delete and recreate the array.
- Synology says RAID, classic or SHR, is not a backup.
- Back up first. Synology says RAID, classic or SHR, is not a backup.[2]
- On Synology, confirm the pool shows Healthy before adding a drive.[3]
- Match the drive type even when sizes differ. Synology does not support HDDs with SSDs, SATA with SAS or NVMe, or 4K native with non-4K native drives in one pool.[3]
- On UGREEN, match the sector format. UGREEN says mixed sector formats in one RAID group may stop the array being created or cut performance, and to ask its customer support to confirm compatibility before buying.[8]
- On QNAP, expect a group of disks with different speeds to run at the speed of the slowest disk.[6]
What to buy, if anything
Answer the questions under "Check your situation" and this section narrows to what your case calls for. Until then every table is shown, each with the case it is for.
NAS drives by price per TB
Why this is here: The drive to add or swap in once the reader knows the size their array type rewards: at least the smallest drive's size on classic RAID, RAID-Z or TRAID (where extra capacity above the smallest drive goes unused), at least the largest drive's size for full use on SHR, and no larger than the parity disk for an Unraid data disk. New 3.5-inch NAS and enterprise hard drives whose maker confirms CMR recording, sorted by price per TB on Amazon.com.
Sources
- Synology: What RAID type is best for my storage? checked 2026-10-14
- Synology: What is Synology Hybrid RAID (SHR)? checked 2026-10-12
- Synology: DSM 7 help, Add Drives to Expand the Storage Pool Capacity checked 2026-10-14
- Synology: DSM 7 help, Replace a Drive checked 2026-10-13
- QNAP: QTS 5.2.x user guide, RAID types checked 2026-10-14
- QNAP FAQ: Can I mix different HDD brands, models, or capacities in a QNAP NAS? checked 2026-10-14
- QNAP FAQ: What are my RAID configuration options when mixing hard drives of different capacities in a QNAP NAS? checked 2026-10-14
- UGREEN: NAS Storage Pool Expansion Guide (Replacing Drives One by One) checked 2026-10-13
- Asustor College: RAID Level Migration and Capacity Expansion checked 2026-10-14
- TerraMaster: The Flexible Disk Array, TRAID checked 2026-10-14
- TerraMaster: TOS 7 help, Storage Pool checked 2026-10-14
- TrueNAS 25.10 documentation: Managing Pools checked 2026-10-13
- TrueNAS documentation: ZFS Primer checked 2026-10-14
- Unraid docs: Getting started checked 2026-10-14
- Unraid docs: Arrays (overview) checked 2026-10-14
- Unraid docs: Adding disks to array checked 2026-10-14
Facts on this page were reviewed on October 14, 2026. Prices and stock are from Amazon.com as of October 14, 2026.