6

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!

Dan
  • 171
  • 3
  • 5
    `How should one approach this?` By not wasting any further time and restoring from backup to a new and better RAID. You also lack details like the type of RAID and platform you use. – Sven Jan 01 '18 at 11:01
  • 3
    Please stop using R5 too, it's 2018 ffs – Chopper3 Jan 01 '18 at 20:00

2 Answers2

5

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.

BaronSamedi1958
  • 12,510
  • 1
  • 20
  • 46
1
  1. As BaronSamedi1958 stated, backup now, all that can still be read. If that's not enough you need to hire a costly recovery specialist.
  2. 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.
  3. Set up a regular backup, according to your scenario and restore requirements.
  4. 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.
  5. 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.
Zac67
  • 8,639
  • 2
  • 10
  • 28
  • Step 1, okay. Step 2, maybe not so much. If he _does_ get a good backup, surely he should not be rebuilding a RAID 5! – Colt Jan 01 '18 at 20:56
  • 1
    RAID5 is dead in the water... – BaronSamedi1958 Jan 01 '18 at 20:59
  • With only four drives and weak NAS hardware there's little choice (that's where step 4 becomes vital). RAID 5 can be OK if you've got a solid backup/restore concept - which you need anyway - and understand its limited reliability. – Zac67 Jan 01 '18 at 21:07
  • Either way, although it there appear to be references to RAID 6 in documentation from at least as early as QTS 4.3.3.0154. And if half the drives are crapping out, probably not a bad time to consider something better. – Colt Jan 01 '18 at 21:21
  • Four-bay QNAP NASes usually support RAID 6 but lacking decent hardware support this can hurt performance significantly. Plus, with four drives you can just as well use RAID 10. – Zac67 Jan 01 '18 at 21:25
  • I have no quibble with RAID 10, or even with another NAS solution. My comment was entirely a question about whether _any_ time should be spent on trying to put back together the RAID 5, rather than trying to get onto something else that is more reliable if a good backup is obtained – Colt Jan 01 '18 at 21:32