Big size of backup file

[fintnovo]

Good day,
I have VM with 120 Gb virtual disk:

Guest operating system (ubuntu linux 12.04 Lts) use only 3,4Gb of disk storage.
But backup file of VM is 26Gb! (with LZO compression)
If I use gzip type compression size of backup file is 17,5Gb
How to reduce size of backup file?
Why backup file size 5-6 times more, than real guest OS data?

 

[dietmar]

Unless you use 'fstrim' inside the VM, the file system may contain random garbage and will increase backup size.

 

[LnxBil]

If TRIM is not supported (due to missing discard option or storage backend that does not support trim), you can use this:

dd if=/dev/zero of=zero bs=64k; sync; sync; sync; rm -f zero

for every real fs based mountpoint.