I have 4 drives assigned to RAID 1 BTRFS cache pool. Everything was fine when I turned the system off to do some maintenance (rearranging cables).
When I turned the system back on, 1 of cache drives (Cache 3) wasn't detected by the system, probably due to loose cable. I noticed this before anything, so I didn't start the array. Surprisingly, unRAID reported 'Configuration is valid', and slot 3 of the cache pool is simply marked as 'Unassigned'.
I turned the system off, and reseated all the cables. After booting up, the missing drive now shows up. But Cache 3 slot is still marked as Unassigned, and the drive that was supposed to be there is now listed under Unassigned Devices.

I would like to seek an advise here on what should I do next? Do i reassign the drive to cache 3 slot? or do I just start the array without cache 3 drive.
Thanks!

 

19 hours ago, ldrax said:

Do i reassign the drive to cache 3 slot?

No, that will be considered a new device, stop the array, if Docker/VM services are using the cache pool disable them, unassign all cache devices, start array to make Unraid "forget" current cache config, stop array, reassign all cache devices, re-enable Docker/VMs if needed, start array.

thank you @johnnie.black

3 hours ago, johnnie.black said:

unassign all cache devices

so, unassign while still leaving all 4 cache slots, right, not setting total number of cache slots to 0?

Either way will work, leave it as is since you're going to add them again later.

Alright, I'll do it shortly.

Is this known issue? Normally if an array disk is missing, its slot will be marked as missing, and upon fixing it physically and reboot, it will show up back on that slot.
I wonder why isn't that the case with cache pool?

Cache pool uses a different logic, but yeah, this behavior could be improved.

 

You still get a warning "all data on this device will be deleted" if for example you added the unassigned device to current pool , like you mentioned on the OP, but it might leave some doubts if it's true when doing this with a previous member, it is, when doing the procedure I described above, you won't get the warning after assigning all the cache devices back, and if a valid pool is detected it will be used.

On 1/20/2020 at 5:19 PM, johnnie.black said:

No, that will be considered a new device,

 

stop the array,

if Docker/VM services are using the cache pool disable them,

unassign all cache devices,

start array to make Unraid "forget" current cache config,

stop array,

reassign all cache devices,

re-enable Docker/VMs if needed,

start array.

I finally get to this, I'm now at step 3: unassign all cache devices. Since there is no 'Unassign' button or drop down, I assume you meant choose 'No Device' next to each of the 4 cache slots. So I chose 'No Device' for the cache 1, 2, 4. As for Cache 3, there no other option other than choosing one of available drives, so I leave it as 'Unassigned'.
So right now, this is how it looks like:
Cache 1: Missing (x)
Cache 2: Missing (x)
Cache 3: Unassigned
Cache 4: Missing (x)

Now before I proceed to 'Start the array', are these states how they are supposed to look like? Just want to make sure

 

6 minutes ago, ldrax said:

are these states how they are supposed to look like?

Yes

Thank you @johnnie.black! I have done all those steps, and now all 4 drives are back in cache pool. Hope nothing changes beneath.