Abnormal backup size

LXD
1

I did a backup/export with:

lxc export toots toots.tar --compression=none --instance-only --optimized-storage

I got a 17G file:

# ls -lha /mnt/storagebox/lxd-backups/toots.tar 
-rw-rw---- 1 root root 17G Sep 12 07:38 /mnt/storagebox/lxd-backups/toots.tar

If I look with zfs list, used space is 9.50G with snapshots:

# zfs list local/containers/toots
NAME                     USED  AVAIL     REFER  MOUNTPOINT
local/containers/toots  9.50G  42.7G     6.72G  /var/snap/lxd/common/lxd/storage-pools/local/containers/toots

Real size on container is 6.80G:

# lxc exec toots -- df -h /
Filesystem              Size  Used Avail Use% Mounted on
local/containers/toots   50G  6.8G   43G  14% /

That’s a bit strange… Is --instance-only really working?
Even if backup/container.bin in the tar file contains snapshots the size seems really wrong.
Maybe --optimized-storage is the culprit? I use ZFS for containers, but my backup storage is a CIFS volume.
Details on the image:

# file backup/container.bin 
backup/container.bin: ZFS shapshot (little-endian machine), version 17, type: ZFS, destination GUID: E6 8A AC 92 EC 39 D3 09, name: 'local/containers/toots@backup-0d19a50d-7733-4e0b-bdd8-ba19c68a39f4'

Any ideas?

2

Is that an uncompressed tar file? If so, compress it to see if it matches the actual sizes.

The issue with tar files is that if you tar a big directory tree with a huge number of small files, then this generates a very large .tar. It is a legacy situation going back several decades.

3

There is only two files in the .tar file so it’s not related to “huge number of small files”.

4

Do you have compression enable in zfs ?

1 Like
5

Definitely a bit surprising as you would expect a disk usage similar to the reference one.

LXD doesn’t really do much magic there, the binary file is just a written down version of a zfs send. So as suggested, it may be related to compression if your on-disk pool is compressed?

1 Like
6

Indeed compression is on! Totally forgot that.

# zfs get compression
NAME                                                                                    PROPERTY     VALUE     SOURCE
local                                                                                   compression  on        local
local/containers                                                                        compression  on        inherited from local
[…]

Thanks and sorry for the noise.