Posts tagged filesystem

BTRFS: filesystem rebalance issues

posted on 2016-04-13 06:38

Sometimes a btrfs filesystem will show wrong usage when df -h is used. This can easily be several GB's. (In my particular case I had 1GB space left, after a rebalance it were 6GB...)

Usually a

btrfs filesystem balance /<path-if-needed>

is all you need to do.

However:

root@sjas:/# btrfs fi bal /
ERROR: error during balancing '/': No space left on device
There may be more info in syslog - try dmesg | tail
root@sjas:/#

May stop you short.

Try:

root@sjas:/# btrfs fi balance start -dusage=10 /
Done, had to relocate 0 out of 33 chunks
root@sjas:/# 

Little more explanation provided by the man page:

    usage=<percent>, usage=<range>
       Balances only block groups with usage under the given percentage. The value of 0 is allowed and will clean up
       completely unused block groups, this should not require any new work space allocated. You may want to use usage=0 in
       case balance is returnin ENOSPC and your filesystem is not too full.

       The argument may be a single value or a range. The single value N means at most N percent used, equivalent to ..N
       range syntax. Kernels prior to 4.4 accept only the single value format. The minimum range boundary is inclusive,
       maximum is exclusive.

Afterwards try re-running btrfs fi bal / for possibly even more available space, or use a bigger value for the usage flag.

btrfs subvolume folder list

posted on 2016-03-27 12:16

A list of good folder candidates for being placed within subvolumes being separate from the root filesystem is here:

  • /boot/grub2/*
  • /opt
  • /srv
  • /tmp
  • /usr/local
  • /var/crash
  • /var/lib/{mailman,named,pgsql,mysql}
  • /var/log
  • /var/opt
  • /var/spool
  • /var/tmp

LVM: shrink volume

posted on 2015-08-07 18:34:25

To shrink a LVM partition, there are several steps to be reproduced:

  • the volume has to be unmounted
  • activate the LVM volumes, so linux can handle them
  • check that the filesystem is error free
  • shrink filesystem, a little more than needed
  • shrink LVM partition
  • expand filesystem to full LVM partition size
  • fsck again, if you are anxious :)

If the volume is mounted, you will not be able to filesystem-check it, or even shrink it. So you can not simply shrink the root partition of your running live system. For this you will need a live disk (google for 'grml linux') and boot from this to make the changes.

So here something to copy paste from:

vgchange -a y
e2fsck -f /dev/<volume_group>/<logical_volume>
resize2fs /dev/<volume_group>/<logical_volume> <size-in-GB-MINUS-1GB>G
lvreduce -L <size-in-GB>G /dev/<volume_group>/<logical_volume>
resize2fs /dev/<volume_group>/<logical_volume>
e2fsck -f /dev/<volume_group>/<logical_volume>

Voila.

Usually you'd want to do this in order to create another volume / partition, but this is stuff for another blogpost.

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