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.
>
> 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
>
>
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