Try "aggr show_space"

----- Original Message ----- From: Stephen C. Losen scl@sasha.acc.virginia.edu To: Borzenkov, Andrey Andrey.Borzenkov@fujitsu-siemens.com Cc: toasters@mathworks.com toasters@mathworks.com Sent: Thu May 22 07:29:53 2008 Subject: Re: "df -h" shows less snapshots than "snap delta"

I am rather puzzled.

cn1:~ # rsh filer df -h vol1 Filesystem total used avail capacity Mounted on /vol/vol1/ 2448GB 776GB 1671GB 32% /vol/vol1/ snap reserve 612GB 158GB 453GB 26% /vol/vol1/..

So according to this we have 156GB worth of snapshots. So far so good.

cn1:~ # rsh filer snap delta vol1

Volume vol1 working...

...

Summary...

From Snapshot To KB changed Time Rate (KB/hour)

---

Oldest_snap Active File System 265800060 14d 09:08 770120.583

Oops. I would expect df -h to show *more* than snap delta (due to the fact that we have more intermediate snapshots); but how comes that - apparently having 260GB worth of snapshot data - I only see 158GB in space accounting?

I am likely missing something obvious. Hmm ... is it possible that "snap delta" accounts for both changed *and* new data while "df -h" accounts for *changed* data only? Looks plausible...

Snapshot accounting can be very tricky I think. Consider this scenario.

1) take snapshot #1 of a volume

2) create a new and very large file

3) take snapshot #2 of volume

4) delete the very large file

5) take snapshot #3

At this point the "delta" between snapshots 1 and 3 and the live volume will be very small. But the "delta" between snapshot 2 and any other snapshot (or the live volume) will be large. This is because snapshot 2 (and only snapshot 2) still contains the large file that was deleted.

So you can see that the delta between the live volume and each of its snapshots does not necessarily increase with the age of the snapshot.

Steve Losen scl@virginia.edu phone: 434-924-0640

University of Virginia ITC Unix Support