Can I Replace One Drive in RAID 5 With a Larger Drive?
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Yes, but on RAID 5 one larger drive adds no usable space by itself. Capacity follows the smallest drive, so with same-size drives the pool grows only after the last one is replaced, one at a time. Synology's SHR works differently: with same-size drives, space grows once two are replaced.
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:
- Pulling a second drive before the first rebuild finishes. Synology allows one replacement at a time, UGREEN says never remove multiple drives at once, and Asustor says replacing several at once, or while the NAS is synchronizing, causes data loss.
- Powering off a QNAP NAS or removing a disk while it synchronizes after Expand Capacity.
- Starting on a pool that is already degraded. UGREEN says the pool must be Normal before you begin.
- Another old drive failing during a swap. UGREEN says each replaced drive leaves the pool degraded with no redundancy. A bad sector or failure on another old drive then may fail the rebuild or the whole pool, and all data may be lost.
- Swapping drives in Basic, JBOD or RAID 0. UGREEN says these cannot be expanded this way and replacing drives in them may lose data.
- Skipping the backup. Synology says RAID, classic or SHR, is not a backup, and both Synology and UGREEN recommend backing up before you start.
- Back up the data before you replace any drive.[1]
- On Synology, run data scrubbing first if the pool supports it, so the volume and pool are Healthy.[1]
- Match the drive type. Synology lets a SATA drive replace only a SATA drive and a SAS drive replace only a SAS drive.[1]
- Check the sector format before buying. UGREEN says mixing 4Kn and 512e drives in one RAID group may stop the array being created or cut performance, and asks you to contact its support first.[5]
- Replace one drive, and wait until the rebuild reaches 100% and the pool is Normal again before the next.[5]
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.
Larger NAS drives by price per TB
Why this is here: The larger drives for a planned swap of every drive in the RAID 5 group (or at least two in SHR), one at a time; on RAID 5 a single larger drive adds no space until the smallest drives are all replaced. New 3.5-inch NAS and enterprise hard drives whose maker confirms CMR recording, sorted by price per TB on Amazon.com.
Frequently asked questions
Is the pool protected while a drive is being replaced?
Not always. Synology says RAID 5 can sustain the loss of a single drive, and UGREEN says the pool has no redundancy while each drive is replaced. Synology's Replace Drive, used with an unused drive, keeps the pool protected by redundancy throughout.
Sources
- Synology: DSM 7 help, Replace a Drive checked 2026-10-13
- Synology: DSM 7 help, What is RAID? checked 2026-10-14
- Synology: What is Synology Hybrid RAID (SHR)? checked 2026-10-12
- QNAP: QTS 5.2.x user guide, Expanding a RAID group by replacing all disks checked 2026-10-13
- UGREEN: NAS Storage Pool Expansion Guide (Replacing Drives One by One) checked 2026-10-13
- Asustor College: RAID Level Migration and Capacity Expansion checked 2026-10-13
Facts on this page were reviewed on October 14, 2026. Prices and stock are from Amazon.com as of October 14, 2026.