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Subject: RE: snapshot autoremove question
Date: Fri, 9 Nov 2007 10:13:20 -0800
Message-ID: <BB375AF679D4A34E9CA8DFA650E2B04E06794BD2@onstor-exch02.onstor.net>
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Thread-Topic: snapshot autoremove question
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References: <BB375AF679D4A34E9CA8DFA650E2B04E06794BB0@onstor-exch02.onstor.net>
From: "Jobi Ariyamannil" <jobi.ariyamannil@onstor.com>
To: "John Keiffer" <john.keiffer@onstor.com>,
	"dl-Design Review" <dl-designreview@onstor.com>
Cc: "Sandrine Boulanger" <sandrine.boulanger@onstor.com>,
	"Vikas Saini" <vikas.saini@onstor.com>,
	"Manohar Divate" <manohar.divate@onstor.com>

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Snapshot auto removal is an optional feature somebody needs to turn on.
If they set the HWM too low, they may end up losing the snapshots.
I don't see any need of setting that below 98%.  The need for removing
snapshots automatically is needed when filesystem operates in close to
full conditions and prevent applications running into ENOSPC because of
the space pinned by snapshots.  By providing an option for the user to
specify that threshold, we ended up with all these interesting
possibilities.
=20
Regards,
Jobi

________________________________

From: John Keiffer=20
Sent: Friday, November 09, 2007 10:05 AM
To: dl-Design Review
Cc: Sandrine Boulanger; Vikas Saini; Manohar Divate
Subject: snapshot autoremove question



[opens mouth]

=20

I would like to understand why we are willing to possibly delete all of
a customer's snapshots, if they have set and reached their autoremoval
high water mark (ARHWM).=20

=20

It seems that if users in the field are keeping a lot of snapshots that
this might not be a problem, since deleting some might free up the
necessary space. If users in the field are only scheduling a smaller
number of snapshots to be taken it is more likely that we might end up
deleting them all.=20

=20

Example problem: I ran it an issue where after creating a large file
(using pre-allocation), my volume usage was over the ARHWM. I then
deleted the large file. However, because both the snapshot deletion and
file deletion happen in the background, the snapshots deletion happened
before the large file was removed and the volume usage went back down.
So I ended up losing my file and my snapshots.

=20

Since we cannot pin weekly, daily, or hourly snapshots, and they are
likely to be the most current, it seems like we should keep at least
one. Some of us in QA think it might be nice to keep one of each, but at
a minimum it seems that we should at least keep the most current. If the
last unpinned snapshot needs to be deleted in order to free up space,
there are bigger issues to deal with.

=20

[inserts foot]

=20

Thank you,

John Keiffer

=20

=20


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<DIV dir=3Dltr align=3Dleft><SPAN class=3D726240718-09112007><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>Snapshot auto removal is an optional feature =
somebody needs=20
to turn on.&nbsp; If they set the HWM too low, they may end up losing =
the=20
snapshots.</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D726240718-09112007><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>I don't see any need of setting that below =
98%.&nbsp; The=20
need for removing snapshots automatically is needed when filesystem =
operates in=20
close to full conditions and prevent applications running into ENOSPC =
because of=20
the space pinned by snapshots.&nbsp; By providing an option for the user =
to=20
specify that threshold, we ended up with all these interesting=20
possibilities.</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D726240718-09112007><FONT =
face=3DArial=20
color=3D#0000ff size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D726240718-09112007><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>Regards,</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D726240718-09112007><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>Jobi</FONT></SPAN></DIV><BR>
<DIV class=3DOutlookMessageHeader lang=3Den-us dir=3Dltr align=3Dleft>
<HR tabIndex=3D-1>
<FONT face=3DTahoma size=3D2><B>From:</B> John Keiffer <BR><B>Sent:</B> =
Friday,=20
November 09, 2007 10:05 AM<BR><B>To:</B> dl-Design Review<BR><B>Cc:</B> =
Sandrine=20
Boulanger; Vikas Saini; Manohar Divate<BR><B>Subject:</B> snapshot =
autoremove=20
question<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=3DSection1>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">[opens=20
mouth]<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">I would like to understand =
why we=20
are willing to possibly delete all of a customer&#8217;s snapshots, if =
they have set=20
and reached their autoremoval high water mark (ARHWM).=20
<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">It seems that if users in =
the field=20
are keeping a lot of snapshots that this might not be a problem, since =
deleting=20
some might free up the necessary space. If users in the field are only=20
scheduling a smaller number of snapshots to be taken it is more likely =
that we=20
might end up deleting them all. <o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P class=3DMsoNormal style=3D"MARGIN-LEFT: 0.5in"><FONT face=3DArial =
size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Example problem: I ran it =
an issue=20
where after creating a large file (using pre-allocation), my volume =
usage was=20
over the ARHWM. I then deleted the large file. However, because both the =

snapshot deletion and file deletion happen in the background, the =
snapshots=20
deletion happened before the large file was removed and the volume usage =
went=20
back down. So I ended up losing my file and my=20
snapshots.<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Since we cannot pin =
weekly, daily,=20
or hourly snapshots, and they are likely to be the most current, it =
seems like=20
we should keep at least one. Some of us in QA think it might be nice to =
keep one=20
of each, but at a minimum it seems that we should at least keep the most =

current.<FONT color=3Dnavy><SPAN style=3D"COLOR: navy"> </SPAN></FONT>If =
the last=20
unpinned snapshot needs to be deleted in order to free up space, there =
are=20
bigger issues to deal with.<FONT color=3Dnavy><SPAN=20
style=3D"COLOR: navy"><o:p></o:p></SPAN></FONT></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
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<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
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