Samtools sort output smaller than input

[Sylphide]

Hello,
I have a problem with samtools sort : my output files are smaller than my input files when they should be identical since only the lines order is changed !
Does anyone know this problem and a solution ?
thanks

[jkbonfield]

It is correct and is caused by higher compression ratios from zlib when data is sorted.

[swbarnes2]

Right, this is normal. You can confirm that yourself by running flagstat on the unsorted and sorted file. They will have the same number of reads.

[Sylphide]

Indeed they have the same read number.
Many thanks for your help !