How Do I Replace My Synology Drives With Larger Drives?
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Swap one drive at a time and let the pool finish its repair before you pull the next; Synology, QNAP, UGREEN and Asustor all say one at a time. The order and count depend on the RAID type: SHR with equal drives grows after two swaps (four for SHR-2), while other RAID types with equal drives grow only after every drive is replaced. Back up first.
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:
- Removing or replacing more than one drive at once. UGREEN and Asustor both warn this can lose data.
- Pulling a drive when there is no spare bay. The pool is Degraded until the repair ends, and UGREEN warns that if another old drive fails in that window, all data may be lost.
- Removing a disk while the RAID group is rebuilding. QNAP warns against it.
- Fitting a drive that still holds files. Everything on the newly added drive is erased when it joins the pool.
- Using a drive not on Synology's compatibility list. Synology says incompatible drives may affect system stability and result in data loss.
- Swapping every drive at once. That means a new pool, and your data comes back only from a backup.
- Back up your data first. Synology says the expansion does not delete data but strongly recommends a backup.[1]
- Use a replacement of the same type as the drive it replaces: SATA for SATA, SAS for SAS, HDD for HDD, SSD for SSD, and 4K native only for 4K native.[1]
- If an unused drive is in the NAS, go to Storage Manager > Storage, click the pool's upper-right icon, then Replace Drive. Remove the smallest drive from the pool, select the new drive, confirm and click Apply. The pool stays protected by redundancy throughout.[1]
- If there is no unused drive and no empty slot, find the smallest drive in Drive Info and deactivate it (HDD/SSD, Action > Deactivate Drive). Power off unless your NAS supports hot-swapping, swap in the larger drive, power on and check it is recognized.[1]
- Repair the storage pool, which will now be in Degraded status, with the new drive.[1]
- Let the pool return to its original status before you start the next drive. Repeat until every drive you planned has been replaced, then check the capacity on the Storage page.[1]
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 hard drives for a one-at-a-time swap
Why this is here: Replacement drives for the swap: each must be the same drive type as the one it replaces and large enough for the pool's RAID type rule (for SHR with mixed sizes, at least as large as the largest drive in the pool). New 3.5-inch SATA NAS and enterprise hard drives whose maker confirms CMR, sorted by price per TB.
Frequently asked questions
How long does each Synology drive swap take?
Synology's pages give no time. If pool usage is above 80 percent, the repair runs in Regular Repair mode instead of the default Fast Repair, which skips unused space. UGREEN gives 10 to 20 hours or longer for rebuilding more than 10 TB on its own NAS, but that is not a Synology figure. The NAS Upgrade Advisor gives a range at a rate you set.
Sources
- Synology DSM 7 help: Replace a Drive checked 2026-10-14
- Synology DSM 6.2 help: Replace Drives to Expand Storage Capacity checked 2026-10-14
- Synology Knowledge Center: How do I expand the storage pool, dual pool, or volume capacity? checked 2026-10-14
- Synology Knowledge Center: Why did the available capacity not increase after I replaced the drives with larger ones? checked 2026-10-14
- Synology Knowledge Center: I added new drives to my Synology NAS, but the available capacity didn't increase. What can I do? checked 2026-10-14
- Synology DSM 7 help: Repair a Storage Pool checked 2026-10-14
- QNAP QTS 5.2 user guide: Expanding a RAID group by replacing all disks checked 2026-10-13
- UGREEN knowledge center: UGREEN NAS Storage Pool Expansion Guide (Replacing Drives One by One) checked 2026-10-13
- Asustor College NAS 352: 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.