I want to know if I have a RAID 5 system that had a failed drive, I replaced it with the wrong drive and it started to rebuild. I need to know if I can pull that drive while it is rebuilding and replace it with a new (and correct) drive and expect it to all rebuild as close to normal as possible?

  • By "replaced it with the wrong drive", did you mean you accidentally swapped out a good drive instead of the failed one? Or did you mean that you swapped out the failed drive with a replacement that you didn't intend to use? – Moses Oct 16 '15 at 1:16
  • no I pulled the failed drive and replaced it with one I didn't intend to use... Slaps me with a salmon – SteveL Oct 16 '15 at 1:29
  • In that case, my answer should apply then. Had you pulled a good drive, you'd be in a sticky situation. – Moses Oct 16 '15 at 1:41
  • have you heard of anyone pulling a drive from a rebuilding raid5 ? – SteveL Oct 16 '15 at 2:22

Yes, it shouldn't be a problem, as long as you are replacing the drive that is currently rebuilding and not another drive. RAID 5 can only suffer one hard drive loss.

After you replace the drive, the rebuilding should restart. I usually swap drives while the system is shut down, just to be safe, but this isn't 100% necessary.

RAID controllers are smart enough to restart or resume rebuilding when they detect the status of the array. If a new drive is there, it will rebuild. If the server is restarted, it will resume on next boot.


It shouldn't be rebuilding at all - you essentially have two failed drives (The dead one, and the one you wrongly replaced) and that's more than raid 5 should be able to handle. Its a wierd situation. I wonder if you have hot spares, and the drive had been replaced quietly, which is the only way I see this working.

I'd suggest letting it rebuild first, and this is the advice we got from the vendor who sold us the disk array. Basically, since there's heavier load on the drives while you rebuild and other drives might fail. Letting it rebuild and replacing the drive means you minimise the load on the disk controllers and reduce the risk of something going on. Doubly so since if you replace the 'wrong' drive, you essentially have two drive failures right now.

Let it rebuild. Swap the 'dead' drive for the 'old' drive that you just pulled, preferably after wiping the old drive. Check your data

Backups would let me sleep better at night should something like this happen.

  • Not sure if you got me correctly, I had 4 drives, one failed, I pulled that one and replaced it with a drive to get it to rebuild but it was accidentally the wrong drive and it too was crashed.. but as per usual, when I put the drive in for it to make 4 drives, it starts automatically to rebuild... so it's essentially rebuilding with another failed drive as the new drive.. I really want to pull it.... and replace it with the new drive but need to make sure it's not going to stuff the rest of the data up as it is currently rebuilding. – SteveL Oct 16 '15 at 1:17
  • It shouldn't be able to rebuild in the situation you described. That's what has me confused. I'm assuming the drive controller/software knows what its doing, and letting it do its thing though. – Journeyman Geek Oct 16 '15 at 1:18
  • well I would have thought that too but it just took 30hrs to go thru a rebuild process on a failed drive and then I accidentally restarted the rebuild process when I rebooted my computer as that turned the system off and on!!! ?!?!? Just about did my head in. I can either wait another 18hrs for it to finish this new (what seems bogus) rebuild, or pull the drive and replace it with the new drive and set it on its new 30hr rebuild... Do you think wait for the current rebuild to finish, or pull it? – SteveL Oct 16 '15 at 1:22
  • Ooh. I think I misunderstood the question. I still wouldn't pull a drive halfway during reconstruction though. – Journeyman Geek Oct 16 '15 at 1:46
  • well that is my worry. MOSES above said it's possible and I would be inclined to believe it is... under normal circumstances... but if I know there is going to be a time when the actual rebuild stops, that allows me to swap the drive safely, and I take your advice, I would possibly be a bit safer no? – SteveL Oct 16 '15 at 2:30

This is very much dependent on the controller (or software) and its behavior. In general, you can pull the failed drive and the replacement drive, insert a new one, and have it rebuild the array.

It does this by calculating parity from the healthy drives, then rebuilding the data on the last. E.g. if you have a 4-drive RAID 5, you have one failed drive, 3 healthy. If you have a 5th drive in that's replacing #4, you can pull 4 and 5.. as long as 3 of the original 4 stay healthy and online.

However, some controllers are quirky. They can have bugs and other issues that complicate it.

If this is a hardware RAID, I'd strongly recommend calling manufacturer support to confirm. They may have some special procedure they want done.

  • Yes it is a PRORAID system, I have emailed the company but they take ages to reply... and this thing is currently rebuilding. – SteveL Oct 16 '15 at 1:31
  • I guess, main question, in a 4 bay raid, I have 3 good drives and one failed drive. the system is currently rebuilding but I don't want it to be. Should I stop it? Should I wait? – SteveL Oct 16 '15 at 1:32
  • It is probably safest to wait. I am not familiar with PRORAID, and it looks like they're fairly low-end. I'd be afraid to stop it or pull the disk. – Bryan Oct 16 '15 at 19:10
  • ok so I have done a trip away to race my bike and come back and it's still in the rebuilding mode?!? something like 49hrs or so?! It's actually looking like I may have to shut it down or pull the disc anyway?! – SteveL Oct 18 '15 at 9:04
  • Yikes, that is slow. Is there a progress indicator? If you have a backup of the data, I'd pull the drive it's rebuilding onto. If you don't have a backup, I'd still try to work with the manufacturer to confirm next steps. – Bryan Oct 19 '15 at 15:44

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