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Subject: RE: snapshot autoremove question
Date: Mon, 12 Nov 2007 08:57:54 -0800
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Thread-Topic: snapshot autoremove question
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From: "Eric Barrett" <eric.barrett@onstor.com>
To: "Tim Gardner" <tim.gardner@onstor.com>,
	"Paul Hammer" <paul.hammer@onstor.com>,
	"Joshua Goldenhar" <joshua.goldenhar@onstor.com>,
	"Henry Lau" <henry.lau@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>,
	"Dennis Arellano" <dennis.arellano@onstor.com>

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I have to add also that I don't agree with the "secondary data loss"
argument.  ARHWM would be elective and therefore no different than any
other cleanup job, such as a Unix system sweeping up files in /tmp, or a
job to delete backup archive images.
=20


________________________________

From: Eric Barrett=20
Sent: Monday, November 12, 2007 8:54 AM
To: Tim Gardner; Paul Hammer; Joshua Goldenhar; Henry Lau; dl-Design
Review
Cc: Sandrine Boulanger; Vikas Saini; Manohar Divate; Dennis Arellano
Subject: RE: snapshot autoremove question


My feedback to Henry before the meeting was that as an admin, I'd be
pissed at the arbitrary requirement that I autogrow stuff before I
automatically delete snapshots.  My own personal preference would be to
delete snapshots first.  I can't imagine I'm the only one.
=20
This is especially true since the implementation was changed so that we
do NOT guarantee the user does not receive ENOSPC because of a
snapshot's disk consumption.
=20
If linking ARHWM and AGHWM increases complexity of the user interaction,
complexity of user understanding, complexity of testing, complexity of
implementation, AND in the end results in a LOSS of functionality, why
do it that way?
=20

________________________________

From: Tim Gardner=20
Sent: Friday, November 09, 2007 11:15 PM
To: Paul Hammer; Joshua Goldenhar; Henry Lau; dl-Design Review
Cc: Sandrine Boulanger; Vikas Saini; Manohar Divate; Dennis Arellano
Subject: RE: snapshot autoremove question


Paul,
=20
This idea was discussed in detail during the design review. The
conclusion was that autogrow and
auto snapshot removal should not be coupled for several reasons.
=20
Coupling them significantly increases the complexity of the design and
implementation.
It will result in more test cases, not less, than the current proposal.
It will increase the complexity of the documentation.
It is more likely to result in support calls.
=20
Consider the workflow where a user sets an ARHWM of 80% with autogrow
disabled.
What do we do when the user later enables autogrow with a 90% HWM?
Do we disable snapshot auro removal because it has a lower HWM?
Do we silently ignore the 80% HWM and instead use a HWM above 90%?
Do we outright change the HWM to something larger then 80%?
De we set if back if autogrow is later disabled?
What HWM do we display to the user when a vol show is done?
=20
It was also thought that customers may want to intentionally set the
ARHWM lower than
the autogrow HWM. Without actually asking customers, we really don't
know.
The consensus was that we should give customers the choice and utilize
the best
practices guide to document implications of various settings.
=20
Tim

=20
________________________________

From: Paul Hammer
Sent: Fri 11/9/2007 8:46 PM
To: Joshua Goldenhar; Henry Lau; dl-Design Review
Cc: Sandrine Boulanger; Vikas Saini; Manohar Divate; Dennis Arellano
Subject: RE: snapshot autoremove question


Hi All,
=20
Like to have the design changed slightly, think that if the user has
autogrow enabled that the HWM to trigger a snapshot deletion cannot be
set to a lower value then the autogrow value (we do not want to lose
secondary data sets, that is essentially data loss), the code must catch
this issue and trigger an error message and prevent the cfg. The
marketing  requirement (not spec) was to free up space by deleting
snapshots if the customer was going to run out of disk space (i.e.
autogrow turned off or out of luns with autogrow on), the requirement
was not about when the deletion should be triggered (at what amount of
capacity was left) or allowing a HWM for activating the deletion. Having
the delete happen before the autogrow adds to many unnecessary test
permutations.  Granted QA must test the condition where AG is set to on
and no free luns are available, if the delete snapshots option is set in
this case then the Snapshot  will be deleted to buy some head room.
=20
Please keep in mind what the requirement stated (not the spec), don't
want to get into a protracted discussion on would we allow snapshots to
be deleted at any HWM, that would be a very different different
requirement.
=20
If the user is going without autogrow being enabled they can set the HWM
to delete snapshots to what ever value they want, would be surprised
that anyone would set it at anything other than 98% or so (given what
the requirment states).
=20
Thanks,
=20
-Paul

________________________________

From: Joshua Goldenhar
Sent: Fri 11/9/2007 1:25 PM
To: Henry Lau; dl-Design Review
Cc: Sandrine Boulanger; Vikas Saini; Manohar Divate; Dennis Arellano
Subject: RE: snapshot autoremove question



Thanks Henry - I see that this mentions the fact that you cannot pin
scheduled snapshots and mentions setting autogrow in such a way that
infers it is independent.

=20

I'm sure Dennis will work his magic to turn this into fabulous
documentation ;-)

-Josh=20

Josh Goldenhar=20
Phone: 408 963 2408, Cell: 408 547 7693=20

________________________________

From: Henry Lau=20
Sent: Friday, November 09, 2007 11:53 AM
To: Joshua Goldenhar; dl-Design Review
Cc: Sandrine Boulanger; Vikas Saini; Manohar Divate
Subject: RE: snapshot autoremove question

=20

Hi Joshua,

=20

Please check the best practice section in section 8.1 of the doc.


=20

/n/software/FileSystem/snapshot_management_R98_autoremove.doc

=20

Thanks,

Henry

=20

________________________________

From: Joshua Goldenhar=20
Sent: Friday, November 09, 2007 11:35 AM
To: Jobi Ariyamannil; John Keiffer; dl-Design Review
Cc: Sandrine Boulanger; Vikas Saini; Manohar Divate
Subject: RE: snapshot autoremove question

=20

Thanks Jobi.

=20

These types of questions came up in the last design review and were
discussed at length.

=20

I think a simple rewording of your problem statement can illuminate the
overall design principle we ended up sticking to:

"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)." Becomes: "...why is the customer willing to
possibly delete all of their snapshots..."

=20

As Jobi mentioned, the customer optionally turns this feature on. It's
our job to make sure the documentation and best practices guides issue
this warning and make operation as clear and understandable as possible.

=20

If we come up with an arbitrary algorithm to preserve snapshots, there
will always be a customer that will say "why did you do it THAT way? - I
would rather have had XYZ..."=20

=20

I did not know we cannot pin the scheduled snapshots - I imagine we'll
get an RFE in the future to auto-pin snapshots or set a preservation
threshold on scheduled snapshots.=20

=20

For now though I really feel the simplicity of the feature as
implemented makes it easy to understand and makes the "dangers" easy to
understand also.

-Josh=20

Josh Goldenhar=20
Phone: 408 963 2408, Cell: 408 547 7693=20

________________________________

From: Jobi Ariyamannil=20
Sent: Friday, November 09, 2007 10:13 AM
To: John Keiffer; dl-Design Review
Cc: Sandrine Boulanger; Vikas Saini; Manohar Divate
Subject: RE: snapshot autoremove question

=20

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

=20

________________________________

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=3D787185616-12112007><FONT =
face=3DArial size=3D2>I=20
have to add also that I don't agree with the "secondary data loss"=20
argument.&nbsp; ARHWM would be elective and therefore no different than =
any=20
other cleanup job, such as a Unix system sweeping up files in /tmp, or a =
job to=20
delete backup archive images.</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D787185616-12112007><FONT =
face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV><FONT face=3DArial =
size=3D2></FONT><BR>
<DIV class=3DOutlookMessageHeader lang=3Den-us dir=3Dltr align=3Dleft>
<HR tabIndex=3D-1>
<FONT face=3DTahoma size=3D2><B>From:</B> Eric Barrett <BR><B>Sent:</B> =
Monday,=20
November 12, 2007 8:54 AM<BR><B>To:</B> Tim Gardner; Paul Hammer; Joshua =

Goldenhar; Henry Lau; dl-Design Review<BR><B>Cc:</B> Sandrine Boulanger; =
Vikas=20
Saini; Manohar Divate; Dennis Arellano<BR><B>Subject:</B> RE: snapshot=20
autoremove question<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D269215116-12112007><FONT =
face=3DArial=20
size=3D2>My feedback to Henry before the meeting was that as an admin, =
I'd be=20
pissed at the arbitrary requirement that I autogrow stuff before I =
automatically=20
delete snapshots.&nbsp; My own personal preference would be to delete =
snapshots=20
first.&nbsp; I can't imagine I'm the only one.</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D269215116-12112007><FONT =
face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D269215116-12112007><FONT =
face=3DArial=20
size=3D2>This is especially true&nbsp;since the implementation was =
changed so that=20
we do NOT guarantee the user does not receive ENOSPC because of a =
snapshot's=20
disk consumption.</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D269215116-12112007><FONT =
face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D269215116-12112007><FONT =
face=3DArial=20
size=3D2>If linking ARHWM and AGHWM increases complexity of the user =
interaction,=20
complexity of user understanding, complexity of testing, complexity of=20
implementation, AND in the end results in a LOSS of functionality, why =
do it=20
that way?</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D269215116-12112007><FONT =
face=3DArial=20
size=3D2></FONT></SPAN>&nbsp;</DIV><BR>
<DIV class=3DOutlookMessageHeader lang=3Den-us dir=3Dltr align=3Dleft>
<HR tabIndex=3D-1>
<FONT face=3DTahoma size=3D2><B>From:</B> Tim Gardner <BR><B>Sent:</B> =
Friday,=20
November 09, 2007 11:15 PM<BR><B>To:</B> Paul Hammer; Joshua Goldenhar; =
Henry=20
Lau; dl-Design Review<BR><B>Cc:</B> Sandrine Boulanger; Vikas Saini; =
Manohar=20
Divate; Dennis Arellano<BR><B>Subject:</B> RE: snapshot autoremove=20
question<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV id=3DidOWAReplyText8728 dir=3Dltr>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Paul,</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>This idea was discussed in =
detail during=20
the design review. The conclusion was that autogrow and</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>auto snapshot removal should =
not be coupled=20
for several reasons.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Coupling them significantly =
increases the=20
complexity of the design and implementation.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>It will result in more test =
cases, not=20
less, than the current proposal.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>It will increase the =
complexity of the=20
documentation.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>It is more likely to result =
in support=20
calls.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Consider the workflow where a =
user sets an=20
ARHWM of 80% with autogrow disabled.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>What do we do when the user =
later enables=20
autogrow with a 90% HWM?</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Do we disable snapshot auro =
removal because=20
it has a lower HWM?</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Do we silently ignore the 80% =
HWM and=20
instead use a HWM above 90%?</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Do we outright change the HWM =
to something=20
larger then 80%?</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>De we set if back if autogrow =
is later=20
disabled?</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>What HWM do we display to the =
user when a=20
vol show is done?</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>It was also thought that =
customers may want=20
to intentionally set the ARHWM lower than</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>the autogrow HWM. Without =
actually asking=20
customers, we really don't know.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>The consensus was that we =
should give=20
customers the choice and utilize the best</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>practices guide to document =
implications of=20
various settings.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr>Tim</DIV>
<DIV dir=3Dltr><BR>&nbsp;</DIV>
<DIV dir=3Dltr>
<HR tabIndex=3D-1>
</DIV>
<DIV dir=3Dltr><FONT face=3DTahoma size=3D2><B>From:</B> Paul =
Hammer<BR><B>Sent:</B>=20
Fri 11/9/2007 8:46 PM<BR><B>To:</B> Joshua Goldenhar; Henry Lau; =
dl-Design=20
Review<BR><B>Cc:</B> Sandrine Boulanger; Vikas Saini; Manohar Divate; =
Dennis=20
Arellano<BR><B>Subject:</B> RE: snapshot autoremove=20
question<BR></FONT><BR></DIV></DIV>
<DIV dir=3Dltr>
<DIV id=3DidOWAReplyText11426 dir=3Dltr>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Hi All,</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Like to have the design =
changed slightly,=20
think that if the user has autogrow enabled that the HWM to trigger a =
snapshot=20
deletion cannot be set to a lower value then the autogrow value (we do =
not want=20
to lose secondary data sets, that is essentially data loss),&nbsp;the =
code must=20
catch this issue and trigger an error message and prevent the cfg. The =
marketing=20
&nbsp;requirement (not spec) was to free up space by deleting snapshots =
if the=20
customer was going to run out of disk space (i.e. autogrow turned off or =
out of=20
luns with autogrow on), the requirement was not about when the deletion =
should=20
be triggered (at what amount of capacity was left) or allowing a HWM for =

activating the deletion. Having the delete happen before the autogrow =
adds to=20
many unnecessary test permutations.&nbsp; Granted QA must test the =
condition=20
where AG is set to on and no free luns are available, if the delete =
snapshots=20
option is set in this case then the Snapshot &nbsp;will be deleted to =
buy some=20
head room.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Please keep in mind what the =
requirement=20
stated (not the spec), don't want to get into a protracted discussion on =
would=20
we allow snapshots to be deleted at any HWM, that would be a very =
different=20
different requirement.</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>If the user is going without =
autogrow being=20
enabled they can set the HWM to delete snapshots to what ever value they =
want,=20
would be surprised that anyone would set it at anything other than 98% =
or so=20
(given what the requirment states).</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Thanks,</FONT></DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV dir=3Dltr><FONT face=3DArial size=3D2>-Paul</FONT></DIV></DIV>
<DIV dir=3Dltr><BR>
<HR tabIndex=3D-1>
<FONT face=3DTahoma size=3D2><B>From:</B> Joshua =
Goldenhar<BR><B>Sent:</B> Fri=20
11/9/2007 1:25 PM<BR><B>To:</B> Henry Lau; dl-Design =
Review<BR><B>Cc:</B>=20
Sandrine Boulanger; Vikas Saini; Manohar Divate; Dennis=20
Arellano<BR><B>Subject:</B> RE: snapshot autoremove=20
question<BR></FONT><BR></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">Thanks Henry =
&#8211; I see=20
that this mentions the fact that you cannot pin scheduled snapshots and =
mentions=20
setting autogrow in such a way that infers it is =
independent.</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I&#8217;m =
sure Dennis will=20
work his magic to turn this into fabulous documentation =
;-)</SPAN></FONT></P>
<DIV>
<P><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">-Josh</SPAN></FONT><FONT=20
color=3Dnavy><SPAN style=3D"COLOR: navy"> </SPAN></FONT></P>
<P><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Josh=20
Goldenhar</SPAN></FONT><FONT color=3Dnavy><SPAN style=3D"COLOR: navy">=20
<BR></SPAN></FONT><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Phone: 408 =
963 2408,=20
Cell: 408 547 7693</SPAN></FONT><FONT color=3Dnavy><SPAN style=3D"COLOR: =
navy">=20
</SPAN></FONT></P></DIV>
<DIV>
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =

face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>
</SPAN></FONT></DIV>
<P class=3DMsoNormal><B><FONT face=3DTahoma size=3D2><SPAN=20
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">From:</SPAN></FONT></B><FONT=20
face=3DTahoma size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma"> Henry Lau=20
<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> Friday, =
November 09,=20
2007 11:53 AM<BR><B><SPAN style=3D"FONT-WEIGHT: bold">To:</SPAN></B> =
Joshua=20
Goldenhar; dl-Design Review<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">Cc:</SPAN></B>=20
Sandrine Boulanger; Vikas Saini; Manohar Divate<BR><B><SPAN=20
style=3D"FONT-WEIGHT: bold">Subject:</SPAN></B> RE: snapshot autoremove=20
question</SPAN></FONT></P></DIV>
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Hi=20
Joshua,</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Please check =
the best=20
practice section in section 8.1 of the=20
doc.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp;=20
</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">/n/software/FileSystem/snapshot_management_R98_autoremove.doc</SPA=
N></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">Thanks,</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">Henry</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"></SPAN></FONT>&nbsp;</P>
<DIV>
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =

face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>
</SPAN></FONT></DIV>
<P class=3DMsoNormal><B><FONT face=3DTahoma size=3D2><SPAN=20
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">From:</SPAN></FONT></B><FONT=20
face=3DTahoma size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma"> Joshua=20
Goldenhar <BR><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> =
Friday,=20
November 09, 2007 11:35 AM<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">To:</SPAN></B>=20
Jobi Ariyamannil; John Keiffer; dl-Design Review<BR><B><SPAN=20
style=3D"FONT-WEIGHT: bold">Cc:</SPAN></B> Sandrine Boulanger; Vikas =
Saini;=20
Manohar Divate<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">Subject:</SPAN></B> RE:=20
snapshot autoremove question</SPAN></FONT></P></DIV>
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Thanks=20
Jobi.</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">These types =
of=20
questions came up in the last design review and were discussed at=20
length.</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I think a =
simple=20
rewording of your problem statement can illuminate the overall design =
principle=20
we ended up sticking to:</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">&#8220;</SPAN></FONT><FONT=20
face=3DArial size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial">I would like=20
to understand why we are willing to possibly delete all of a =
customer&#8217;s=20
snapshots, if they have set and reached their autoremoval high water =
mark=20
(ARHWM).&#8221; <FONT color=3D#333399><SPAN=20
style=3D"COLOR: #333399">Becomes:</SPAN></FONT> &#8220;&#8230;why is the =
customer willing to=20
possibly delete all of their snapshots&#8230;&#8221;<FONT =
color=3Dnavy><SPAN=20
style=3D"COLOR: navy"></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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">As Jobi =
mentioned, the=20
customer optionally turns this feature on. It&#8217;s our job to make =
sure the=20
documentation and best practices guides issue this warning and make =
operation as=20
clear and understandable as possible.</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">If we come up =
with an=20
arbitrary algorithm to preserve snapshots, there will always be a =
customer that=20
will say &#8220;why did you do it THAT way? &#8211; I would rather have =
had XYZ&#8230;&#8221;=20
</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I did not =
know we=20
cannot pin the scheduled snapshots &#8211; I imagine we&#8217;ll get an =
RFE in the future to=20
auto-pin snapshots or set a preservation threshold on scheduled =
snapshots.=20
</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">For now =
though I really=20
feel the simplicity of the feature as implemented makes it easy to =
understand=20
and makes the &#8220;dangers&#8221; easy to understand =
also.</SPAN></FONT></P>
<DIV>
<P><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">-Josh</SPAN></FONT><FONT=20
color=3Dnavy><SPAN style=3D"COLOR: navy"> </SPAN></FONT></P>
<P><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Josh=20
Goldenhar</SPAN></FONT><FONT color=3Dnavy><SPAN style=3D"COLOR: navy">=20
<BR></SPAN></FONT><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Phone: 408 =
963 2408,=20
Cell: 408 547 7693</SPAN></FONT><FONT color=3Dnavy><SPAN style=3D"COLOR: =
navy">=20
</SPAN></FONT></P></DIV>
<DIV>
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =

face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>
</SPAN></FONT></DIV>
<P class=3DMsoNormal><B><FONT face=3DTahoma size=3D2><SPAN=20
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">From:</SPAN></FONT></B><FONT=20
face=3DTahoma size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma"> Jobi=20
Ariyamannil <BR><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> =
Friday,=20
November 09, 2007 10:13 AM<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">To:</SPAN></B>=20
John Keiffer; dl-Design Review<BR><B><SPAN=20
style=3D"FONT-WEIGHT: bold">Cc:</SPAN></B> Sandrine Boulanger; Vikas =
Saini;=20
Manohar Divate<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">Subject:</SPAN></B> RE:=20
snapshot autoremove question</SPAN></FONT></P></DIV>
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dblue size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">Snapshot auto =
removal=20
is an optional feature somebody needs to turn on.&nbsp; If they set the =
HWM too=20
low, they may end up losing the snapshots.</SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dblue size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">I don't see =
any need of=20
setting that below 98%.&nbsp; The need for removing snapshots =
automatically is=20
needed when filesystem operates in close to full conditions and prevent=20
applications running into ENOSPC because of the space pinned by =
snapshots.&nbsp;=20
By providing an option for the user to specify that threshold, we ended =
up with=20
all these interesting possibilities.</SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dblue size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: =
Arial">Regards,</SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dblue size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: =
Arial">Jobi</SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =

face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>
</SPAN></FONT></DIV>
<P class=3DMsoNormal style=3D"MARGIN-BOTTOM: 12pt"><B><FONT =
face=3DTahoma size=3D2><SPAN=20
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">From:</SPAN></FONT></B><FONT=20
face=3DTahoma size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma"> John=20
Keiffer <BR><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> =
Friday, November=20
09, 2007 10:05 AM<BR><B><SPAN style=3D"FONT-WEIGHT: bold">To:</SPAN></B> =
dl-Design=20
Review<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Cc:</SPAN></B> Sandrine =
Boulanger;=20
Vikas Saini; Manohar Divate<BR><B><SPAN=20
style=3D"FONT-WEIGHT: bold">Subject:</SPAN></B> snapshot autoremove=20
question</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">[opens=20
mouth]</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"></SPAN></FONT>&nbsp;</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). =
</SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT>&nbsp;</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. </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"></SPAN></FONT>&nbsp;</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 =
snapshots.</SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT>&nbsp;</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"></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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">[inserts=20
foot]</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"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Thank =
you,</SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">John =
Keiffer</SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
style=3D"FONT-SIZE: =
12pt"></SPAN></FONT>&nbsp;</P></DIV></DIV></DIV></BODY></HTML>

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