Question Re-add original good drive into RAID 5 after new disk failed to expand/rebuild ?

[Andy141]

I have tried to increase the HDD size in a raid 5 array (4 x 6TB disks) on a 4 disk QNAP TS439Pro 2+. I followed the QNAP expanding procedure for the hot swap of the drives and initially removed disk 1 in slot 1 and installed a new 8tb drive the system started rebuilding but then it found I/O errors on disk 4 and has been showing "rebuilding 0%” for the last 2 days and 7 hours. When I interrogate the CPU it is running on average at 1.5%. I assume the system has hung.

Can I remove the new 8tb disk in slot 1 and replace it with the 6tb disk that was in this slot originally. Will this put the array back into a working state so I can then remove the faulty disk in slot 4 and attempt to rebuild the array again. Or will the system try to wipe the original 6 TB disk and rebuild? If it does this it would destroy the existing RAID 5 data on the disk. I have not added or removed any files from the volume since this started so hopefully the RAID 5 data on the disks in slots 2 to 4 should not have altered since the rebuilding started, unless the data on these disks is altered by the rebuilding process?

 

[USAFRet]

1. This is specifically what a good backup is for.

2. Unknown if this will work. A RAID 5 can survive loss of one drive, assuming no other problems. Take out the bad, put in a new good one, it rebuilds.
But, since yours has been "rebuilding" for 2 days, with potentially 2 missing members...the new 8TB and the existing potentially failing 6TB...all bets are off.

3. See #1. Especially inn the context of a major hardware swap like this.

Some years ago, I bumped my QNAP RAID 5 from 4x 3TB to 4x 4TB. One drive at a time. With about 6TB data in the array, rebuild time was was about 7 hours for each new drive and rebuild.
Upon seeing the final 4TB, the array increased in size.
But I only did this with a known good offline backup of the entire contents.

 

[Andy141]

1. This is specifically what a good backup is for.

2. Unknown if this will work. A RAID 5 can survive loss of one drive, assuming no other problems. Take out the bad, put in a new good one, it rebuilds.
But, since yours has been "rebuilding" for 2 days, with potentially 2 missing members...the new 8TB and the existing potentially failing 6TB...all bets are off.

3. See #1. Especially inn the context of a major hardware swap like this.

Some years ago, I bumped my QNAP RAID 5 from 4x 3TB to 4x 4TB. One drive at a time. With about 6TB data in the array, rebuild time was was about 7 hours for each new drive and rebuild.
Upon seeing the final 4TB, the array increased in size.
But I only did this with a known good offline backup of the entire contents.

Thanks for getting back so promptly really appreciated.

The NAS is backed up to another NAS, I may just loose changes over the last week or two which won't be a big deal.

I have not written or read any information from the NAS since I started the expansion.
But I am unsure whether the actual expansion/rebuild process would alter the information on the other drives in slots 2 to 4.
If all the process does is write data to the new drive in slot 1 and the data on the other drives in the NAS is not altered then I would have thought replacing the new drive with the original drive which is good may bring the raid back alive.
QNAP support have just come back with the suggestion of shutting down the NAS then remove the new drive in slot 1 and replace with original good drive that was in this location and restart.
I am just a little hesitant until I understand how the RAID expansion/rebuild effects the other drives so I can get piece of mind

 

[USAFRet]

But I am unsure whether the actual expansion/rebuild process would alter the information on the other drives in slots 2 to 4.

Yes, probably it does.

But try what QNAP says, and see what happens.

 

[Andy141]

Yes, probably it does.

But try what QNAP says, and see what happens.

It looks as though the only way forward is to swap the disk back and hope.
I will keep you updated with progress so at least the information can be shared with other users on the forum.
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