Fix RAID 5 with two drives containing bad blocks [closed]
Assume the following situation: An administrator was not careful enough maintaining a NAS server (QNAP QTS 4.3.3) using RAID5 and it has already reached a situation in which two (out of four) drives contain bad blocks, however no drive failed completely. There's no external backup.
Assuming that the bad blocks on the two drives don't overlap, it makes sense that 100% data recovery should be possible, but is that really so? How should one approach this?
Thanks all!
Backup ASAP. If you want to be 100% sure you'd better hire some recovery service. It's going to cost you some $$$ but you decide does it worth it or not.
- As BaronSamedi1958 stated, backup now, all that can still be read. If that's not enough you need to hire a costly recovery specialist.
- Replace the failed disks, first one and after (hopefully successfull) rebuild the other. Depending on the exact controller logic, a full data check may be a better solution to repair the damage before replacing the disks. You should contact vendor support to help you decide on that.
- Set up a regular backup, according to your scenario and restore requirements.
- Reconsider whether a low-cost NAS fits your requirements in performance and reliability - few, large disks are cheap but cause extensive rebuild periods when one fails.
- Make sure you set up regular disk scrubbing aka media patrol. This makes sure no stale sectors build up that pop up on a rebuild and make it fail.