Re: enospc errors during balance — how to prevent out of space

[Leszek Dubiel <leszek@dubiel.pl>]

Final report for "no space" and balancing.
I write it for maybe it will help someone.


My problem was identical to this one:

https://superuser.com/questions/1573030/cannot-repair-btrfs-partition-because-there-is-too-little-space-left



While mounting it went "read only" because of errors:

         errs: wr: 0, rd 0, flush 0, corrupt: 35967, gen 0

         "No space left failed to recover relocation"

         space_info: metadata ... is full



On "read only" you cannot add more devices, you canot finish balance.



Tried to repair system — no errors.



It was done on terminal, co I uploaded photos here:

https://postimg.cc/gallery/09dzGRG



Finally I have cleared disks and start to rebuild system from scratch.





Balancing script reworked to start balancing earlier and slower,
then go faster:



     findmnt --types btrfs --output SOURCE --nofsroot --noheadings | 
sort | uniq |
     while read dev; do

         # mount point
         mnt=$(findmnt --source "$dev" --output TARGET --first-only 
--noheadings)
         test -d "$mnt" || continue

         # lowest unallocated space from all disks in btrfs filesystem
         una=$(
             btrfs dev usage "$mnt" -g |
             sed -nr 's/.*Unallocated: +([0-9]+)\.[0-9]{2}GiB.*/\1/; T; p' |
             sort -n | head -n1
         )
         echo -n "$una" | tr -c "[[:print:]]" "#" | grep -Eq '^[0-9]+$' 
|| continue

         # if lots of unallocated space do nothing
         if test "$una" -ge 32; then
             : # do nothing

         # if going low, then optimize "dusage" slowly
         elif test "$una" -ge 16; then
             seq --format "-dusage=%g,limit=2" 0 20 100

         elif test "$una" -ge 8; then
             seq --format "-dusage=%g,limit=3" 0 10 100

         # if critically low, then balnace both "dusage" and "musage"
         else
             seq --format "-dusage=%g,limit=4" 0 10 100
             seq --format "-musage=%g,limit=1" 0 10 100
         fi |

         # balance for options above until any extents rellocated
         while read opt; do

             btrfs balance start "$opt" "$mnt" 2>&1 |
             grep -Eq "Done, had to relocate [1-9][0-9]* out of [0-9]+ 
chunks" &&

             # if relocated, then get out of two loops for next "$dev"
             break 2
         done
     done