Version is 7.2.4P6.
С уважением / With best regards / Mit freundlichen Grüβen
--- Andrey Borzenkov Senior system engineer
-----Original Message----- From: George T Chen [mailto:gtchen@yahoo-inc.com] Sent: Thursday, May 22, 2008 11:48 PM To: Stephen C. Losen; Borzenkov, Andrey Cc: toasters@mathworks.com Subject: RE: "df -h" shows less snapshots than "snap delta"
What version of OnTap are you running? I have found that versions up to at least 7.1 to be inaccurate in their delta measurement.
-----Original Message----- From: owner-toasters@mathworks.com
[mailto:owner-toasters@mathworks.com]
On Behalf Of Stephen C. Losen Sent: Thursday, May 22, 2008 4:30 AM To: Borzenkov, Andrey Cc: toasters@mathworks.com 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.
take snapshot #1 of a volume
create a new and very large file
take snapshot #2 of volume
delete the very large file
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