[[SOLVED] Rebuild Cache Pool]

Ahh i see - that was some quick "Just In Time" save you did there.

It worked, through whatever magic removal and adding back in does, the cache is back online

 

Because i was worried on starting up the array again, i was trying to find a spare external HDD to transfer the data out 😅 so this really saved me alot of time

 

Thanks @JorgeB

[[SOLVED] Rebuild Cache Pool]

Faced a similar experience when a reboot with a bad sata card occured. Knocking out my entire cache array.

 

Because no actual drives was lossed, after rewiring to another sata port (SATA 2 sadly). I am able to see the entire "btrfs filesystem" even if I unable to add them back to unraid (as they are unassigned, and shows a warning that all data will be formatted when reassigning)

 

$ btrfs filesystem show
Label: none  uuid: 0bfdf8d7-1073-454b-8dec-5a03146de885
        Total devices 6 FS bytes used 1.37TiB
        devid    2 size 111.79GiB used 37.00GiB path /dev/sdo1
        devid    3 size 223.57GiB used 138.00GiB path /dev/sdm1
        devid    4 size 223.57GiB used 138.00GiB path /dev/sdi1
        devid    5 size 1.82TiB used 1.60TiB path /dev/sdd1
        devid    6 size 1.82TiB used 1.60TiB path /dev/sde1
        devid    7 size 111.79GiB used 37.00GiB path /dev/sdp1
        
 ... there are probably other BTRFS disk drives if you have theme as well ...

 

While attempting to remount this cache pool using the steps found at 

I was unfortunately faced with an error of 

$ mount -o degraded,usebackuproot,ro /dev/sdo1 /dev/sdm1 /dev/sdi1 /dev/sdd1 /dev/sde1 /dev/sdp1  /recovery/cache-pool
mount: bad usage

 

 

So alternatively I mount using the UUID (with /recovery/cache-pool being the the recovery folder i created)

 

$ mount -o degraded,usebackuproot,ro --uuid 0bfdf8d7-1073-454b-8dec-5a03146de885  /recovery/cache-pool

 

With that i presume i can then safely remove the drives from the cache pool (for the last 2 disk that was left), and slowly manually reorganize and recover the data.

 

[Disable auto array start when there's a disk missing]

Chiming in here - my situation was a sata card failure, which was replaced - however between the reboots the auto start pretty much killed the cache the same way as 

 

https://forums.unraid.net/topic/94233-solved-rebuild-cache-pool/

 

So despite having no disk failure itself, im now trying to figure out how to rebuild the whole btrfs array to migrate my approximately 2TB of VM data that i have pinned to be exclusively on cache 😅

 

My guess is that, because no drives were really lost, i should be able to perform the recovery in the next 24 hours - but it isn't exactly a pleasant experience, needing to time sink into the recovery process due to such an issue.

My array is now with disabled auto-start, auto-start really should not be default behaviour, if there is a risk of permemenant data loss - which we would block from the UI and warn normally anyway.