Use proper trim block size
Use proper trim block size

(cherry picked from commit ccdffc103f4dee506d11ecb8f5891435ab9f1031)

uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend