Can I replace a failed Synology drive with a bigger one?

Replacing a failed drive with a larger one is fully supported and often the sensible move: bigger drives are cheaper per terabyte and leave headroom. The nuance is when the extra capacity becomes usable, which depends on your RAID type.

SHR and the "largest drive" rule

Synology Hybrid RAID (SHR) is the most flexible: you can drop in a larger drive and the pool repairs immediately, using the new drive at the size needed to rebuild. To grow the volume, SHR needs the array's capacity maths to change: with equal-size drives you typically need to replace two drives with larger ones before usable space increases, because SHR's protection is sized against the largest drive. Replace them one at a time, letting the pool repair fully between swaps.

RAID 5 and RAID 6

Classic RAID 5/6 sizes every drive to the smallest member. A single larger replacement rebuilds fine but its extra space sits unused until every drive in the array is at least that size: then you can expand the volume. So a bigger drive is never wrong, it just may not add space yet.

How to do it safely

1. Confirm the pool is only degraded, not crashed (a degraded pool is still protected against no further failures).
2. Insert the larger drive in the failed bay: hot-swap on models with hot-swappable bays, otherwise power down first.
3. In Storage Manager, choose Repair and select the new drive.
4. Let the rebuild finish completely before touching another drive: a second failure during the rebuild is the real risk.

Buy a CMR NAS drive at least as large as the drive it replaces (never SMR: it can stall the rebuild). The table below lists in-stock CMR drives by price per terabyte.