Can I use my NAS during a RAID rebuild?

You can keep using the NAS while it rebuilds: the array is degraded but online, so your files stay accessible. The question is whether you should load it heavily, and the answer is no.

Why light use is better

A rebuild and your file access compete for the same drives. The busier you keep the NAS, the slower the rebuild goes, and the rebuild is a window where a single-parity array (RAID 5 / SHR) has no remaining fault tolerance. A second drive failing before it finishes crashes the pool. Every extra hour of rebuild is extra exposure, so finishing quickly is a safety matter, not just convenience.

Practical guidance

• Light reads are fine: streaming a file, checking a document.
• Avoid heavy writes: large copies, big backups, bulk imports; defer them until the rebuild completes.
• Do not remove any other drive, and do not start another maintenance job.
• Leaving it idle is the fastest, safest path to a finished rebuild.

If it must stay busy

For a business that cannot pause, this is the argument for RAID 6 / SHR-2: double parity keeps you protected through the rebuild even under load. Use CMR drives so the rebuild is not needlessly slow. The table lists in-stock CMR drives.