Hi,

I'm on Unraid 7.1.2. I have setup and used a 3x18TB HDD RAIDZ1 ZFS pool successfully, all great and happy!

Yesterday I got a SMART notification that one of the disks is loosing HELIUM - no idea why, but ok. I have a spare identical drive so I want to switch to that.

Turned the server off last night, watched a youtube video before sleeping and now wanted to do that.

I attached the spare disk to the server and booted. Unfortunately, the failed HDD is no longer detected by Unraid. I attached the disk via USB - it is found, but shows a size of 0 byte - so it's dead.

How do I go about this? Do I - as described in above video - simply add the spare disk to the ZFS pool and start the array, which then automagically triggers resilvering and restores the data? The text "All existing data on this device will be OVERWRITTEN when array is Started" lets me assume that is the case.

But I'd rather like to know if that is the correct way before I make matters even worse...

Thx!

Edited July 12, 2025Jul 12 by MichaelAnders2

1 hour ago, MichaelAnders2 said:

simply add the spare disk to the ZFS pool and start the array, which then automagically triggers resilvering and restores the data?

Basically yes, more details here:

https://forums.unraid.net/topic/46802-faq-for-unraid-v6/#findComment-480419

Thanks, JorgeB!

As I am scared sh*tl*ess of more data loss, one follow up question concerning "Always a good idea to backup anything important on the current pool in case something unexpected happens" and the "Procedure if you can have both the old and new devices connected at the same time" you described - os the backup something I should have done or something I can still do?

My guess is the latter. And the message "Start will remove the missing pool disk and then bring the array on-line." just means that:

1. the disk 2 slot will remain as "no device"

2. disk 1 and disk 3 will simulate data from disk 2 - no resilvering yet (as that might cause corruption), not sure if that pool is read only (probably not needed, but not a good idea to write on it)?

3. backup the important data elsewhere

4. once done stop the array

5. add the new disk as disk 2

6. start the array

7. wait for the resilvering to complete

8. use the system as normal

Is this assumption correct or do I go straight to point 5?

8 minutes ago, MichaelAnders2 said:

os the backup something I should have done or something I can still do?

You should always have a backup of anything important, you could still do the backup now by mounting the pool degraded.

11 minutes ago, MichaelAnders2 said:

And the message "Start will remove the missing pool disk and then bring the array on-line." just means that:

Yes, it will mount the pool degraded, if there's only a very small percentage of data that you want to backup, it may be worth doing the backup first. To back the whole pool, you might as well replace the disk now and backup after, to get the pool healthy ASAP.

Great, thanks a lot for your help!!!

Backups are done of important stuff, just not in the last few days for some files/folders... need another machine for automation (coming soon...)