topic Re: Dump backup estimated size differ from actual used size ?? in ONTAP Discussions

Dump backup estimated size differ from actual used size ??

sdjoshi75 — Thu, 05 Jun 2025 07:04:07 GMT

I am using dump command to backup data on tape. But estimated and backed up data through dump command is more than the existing used data on MKT volume

in dump log file it show estimated 2154459967 KB(2054GB ) of data to be backed up instead of this actual used data is 1459GB + 7GB snapshot.

Volume size
#df -h MKT
Filesystem                       total           used       avail capacity    Mounted on
/vol/MKT/                          2823GB     1450GB     1372GB            52% /vol/MKT/
/vol/MKT/.snapshot       705GB       7617MB      698GB       1% /vol/MKT/.snapshot

*****************

NetApp-001>dump 0f null /vol/MKT

DUMP: creating "/vol/MKT/../snapshot_for_backup.995" snapshot.

DUMP: Using Full Volume Dump

DUMP: Dumping tape file 1 on null

DUMP: Date of this level 0 dump: Thu Dec 2 28:11:51 2010.

DUMP: Date of last level 0 dump: the epoch.

DUMP: Dumping /vol/MKT to null

DUMP: mapping (Pass I)[regular files]

DUMP: mapping (Pass II)[directories]

DUMP: estimated 2154459967 KB.
CAN ANYONE PLEASE CLEARIFY WHY ITS SHOWING DESCRIPANCY IN DATA BACKUP through dump ???????????

Re: Dump backup estimated size differ from actual used size ??

kritchie — Fri, 03 Dec 2010 05:43:38 GMT

Any chance you're running dedupe on the volume?

Re: Dump backup estimated size differ from actual used size ??

sdjoshi75 — Fri, 03 Dec 2010 06:00:17 GMT

Yes dedup is enabled on this volume

Re: Dump backup estimated size differ from actual used size ??

sdjoshi75 — Fri, 03 Dec 2010 07:38:13 GMT

Hi kent what I observe is that MKT volume is showing 610 GB saved space through df -sh .. Can it be the reason the estimated dump size is more 1450+610 (2060GB) that actual used size ??????

# sis status
Path State Status Progress
/vol/MKT Enabled Idle Idle for 120:38:20

# df -sh
Filesystem used saved %saved

/vol/MKT/ 1450GB 610GB 29%

Re: Dump backup estimated size differ from actual used size ??

kritchie — Fri, 03 Dec 2010 11:32:22 GMT

Right. Dedupe is not preserved when going to tape with NDMP. So if you take the estimate in KB and divide by 1024 twice, you're within a couple of GB of your used plus saved calculation. It is an estimate afterall.

Re: Dump backup estimated size differ from actual used size ??

kritchie — Fri, 03 Dec 2010 11:49:37 GMT

I know I said NDMP but dump works the same way. See KB2013579 on the NOW site.