topic NDMP backup size difference in ONTAP Discussions

NDMP backup size difference

TWINKLE_XEROX — Thu, 05 Jun 2025 06:07:03 GMT

I am taking NDMP backup (through Netbackup) of volume which is designated as snapvault destination.

Volume size is showing as

Filesystem total used avail capacity Mounted on

/vol/sv_A/ 500GB 258GB 241GB 52% /vol/sv_A/

/vol/sv_A/.snapshot 0GB 17GB 0GB ---% /vol/sv_A/.snapshot

Volume State Status Options

sv_A online raid_dp, flex nosnap=on, create_ucode=on,

32-bit fractional_reserve=0

Volume UUID: 9563bcde-492d-11df-b1be-00a09812ec9e

Containing aggregate: 'aggr7'

In Netbackup backup selection is /vol/sv_A/ and backup size I am getting is 251627840 KB. There is almost 7 GB difference (less) in backup size. I am not able to understand the gap.

Thanks in advance !!!

Re: NDMP backup size difference

billshaffer — Thu, 21 Mar 2013 15:56:36 GMT

df is not an accurate measure of how much space is taken by data. If I recall it is also calculating allocated space - that is, if your block size is 4k, and you have a file that is 1k, the entire 4k is allocated on disk. That extra 3k is reported in df, but NetBackup doesn't back up the white space, and so reports the sum of the actual data.

A difference of 7G from 258G doesn't strike me as out of the ordinary. If you want to be sure you can try summing the size of each file (which is rather tedious). You can also try seeing what quotas show, though I'd have to see exactly how quotas report data - they may suffer from the same issue. If you have the space, as a sanity check you can try restoring the data to another volume - you'll probably still see a difference, but (probably) not as big, due to fragmented files in the original copy.

Hope that helps

Bill