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Subject: RE: snapshot autoremove question
Date: Sat, 10 Nov 2007 09:26:25 -0800
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Thread-Topic: snapshot autoremove question
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From: "Paul Hammer" <paul.hammer@onstor.com>
To: "Tim Gardner" <tim.gardner@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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Thanks Tim. I was aware of this (email content).
=20
The main thing to me is that the spec when way beyond what the =
requirement asked for and made thing much more complex then necessary. I =
think we can live with this as long as for the autogrow user we always =
remove snapshots after the autogro event, which should be never if they =
are configured correctly.
=20
Thanks.
=20
-Paul

________________________________

From: Tim Gardner
Sent: Fri 11/9/2007 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

=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 id=3DidOWAReplyText3430 dir=3Dltr>=0A=
<DIV dir=3Dltr><FONT face=3DArial color=3D#000000 size=3D2>Thanks Tim. I =
was aware of this (email content).</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial color=3D#000000 =
size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial color=3D#000000 size=3D2>The main =
thing to me is that the spec when way beyond what the requirement asked =
for and made thing much more complex then necessary. I think we can live =
with this as long as for the autogrow user we always remove snapshots =
after the autogro event, which should be never if they are configured =
correctly.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Thanks.</FONT></DIV>=0A=
<DIV dir=3Dltr>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>-Paul</FONT></DIV></DIV>=0A=
<DIV dir=3Dltr><BR>=0A=
<HR tabIndex=3D-1>=0A=
<FONT face=3DTahoma size=3D2><B>From:</B> Tim Gardner<BR><B>Sent:</B> =
Fri 11/9/2007 11:15 PM<BR><B>To:</B> Paul Hammer; Joshua Goldenhar; =
Henry Lau; dl-Design Review<BR><B>Cc:</B> Sandrine Boulanger; Vikas =
Saini; Manohar Divate; Dennis Arellano<BR><B>Subject:</B> RE: snapshot =
autoremove question<BR></FONT><BR></DIV>=0A=
<DIV dir=3Dltr>=0A=
<DIV id=3DidOWAReplyText8728 dir=3Dltr>=0A=
<DIV dir=3Dltr><FONT face=3DArial color=3D#000000 =
size=3D2>Paul,</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>This idea was discussed in =
detail during the design review. The conclusion was that autogrow =
and</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>auto snapshot removal should =
not be coupled for several reasons.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Coupling them significantly =
increases the complexity of the design and implementation.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>It will result in more test =
cases, not less, than the current proposal.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>It will increase the =
complexity of the documentation.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>It is more likely to result =
in support calls.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Consider the workflow where a =
user sets an ARHWM of 80% with autogrow disabled.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>What do we do when the user =
later enables autogrow with a 90% HWM?</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Do we disable snapshot auro =
removal because it has a lower HWM?</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Do we silently ignore the 80% =
HWM and instead use a HWM above 90%?</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Do we outright change the HWM =
to something larger then 80%?</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>De we set if back if autogrow =
is later disabled?</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>What HWM do we display to the =
user when a vol show is done?</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>It was also thought that =
customers may want to intentionally set the ARHWM lower than</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>the autogrow HWM. Without =
actually asking customers, we really don't know.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>The consensus was that we =
should give customers the choice and utilize the best</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>practices guide to document =
implications of various settings.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr>Tim</DIV>=0A=
<DIV dir=3Dltr><BR>&nbsp;</DIV>=0A=
<DIV dir=3Dltr>=0A=
<HR tabIndex=3D-1>=0A=
</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DTahoma size=3D2><B>From:</B> Paul =
Hammer<BR><B>Sent:</B> Fri 11/9/2007 8:46 PM<BR><B>To:</B> Joshua =
Goldenhar; Henry Lau; dl-Design Review<BR><B>Cc:</B> Sandrine Boulanger; =
Vikas Saini; Manohar Divate; Dennis Arellano<BR><B>Subject:</B> RE: =
snapshot autoremove question<BR></FONT><BR></DIV></DIV>=0A=
<DIV dir=3Dltr>=0A=
<DIV id=3DidOWAReplyText11426 dir=3Dltr>=0A=
<DIV dir=3Dltr><FONT face=3DArial color=3D#000000 size=3D2>Hi =
All,</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial color=3D#000000 =
size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial color=3D#000000 size=3D2>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),&nbsp;the code must catch this =
issue and trigger an error message and prevent the cfg. The marketing =
&nbsp;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.&nbsp; =
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 &nbsp;will be deleted to buy some head =
room.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>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.</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>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).</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>Thanks,</FONT></DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>=0A=
<DIV dir=3Dltr><FONT face=3DArial size=3D2>-Paul</FONT></DIV></DIV>=0A=
<DIV dir=3Dltr><BR>=0A=
<HR tabIndex=3D-1>=0A=
<FONT face=3DTahoma size=3D2><B>From:</B> Joshua =
Goldenhar<BR><B>Sent:</B> Fri 11/9/2007 1:25 PM<BR><B>To:</B> Henry Lau; =
dl-Design Review<BR><B>Cc:</B> Sandrine Boulanger; Vikas Saini; Manohar =
Divate; Dennis Arellano<BR><B>Subject:</B> RE: snapshot autoremove =
question<BR></FONT><BR></DIV>=0A=
<DIV>=0A=
<DIV class=3DSection1>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Thanks Henry =
&#8211; 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.</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I&#8217;m =
sure Dennis will work his magic to turn this into fabulous documentation =
;-)</SPAN></FONT></P>=0A=
<DIV>=0A=
<P><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FONT-SIZE: =
10pt; COLOR: navy; FONT-FAMILY: Arial">-Josh</SPAN></FONT><FONT =
color=3Dnavy><SPAN style=3D"COLOR: navy"> </SPAN></FONT></P>=0A=
<P><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FONT-SIZE: =
10pt; COLOR: navy; FONT-FAMILY: Arial">Josh Goldenhar</SPAN></FONT><FONT =
color=3Dnavy><SPAN style=3D"COLOR: navy"> <BR></SPAN></FONT><FONT =
face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FONT-SIZE: 10pt; =
COLOR: navy; FONT-FAMILY: Arial">Phone: 408 963 2408, Cell: 408 547 =
7693</SPAN></FONT><FONT color=3Dnavy><SPAN style=3D"COLOR: navy"> =
</SPAN></FONT></P></DIV>=0A=
<DIV>=0A=
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =
face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">=0A=
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>=0A=
</SPAN></FONT></DIV>=0A=
<P class=3DMsoNormal><B><FONT face=3DTahoma size=3D2><SPAN =
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">From:</SPAN></FONT></B><FONT face=3DTahoma size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> Henry Lau <BR><B><SPAN =
style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> Friday, November 09, 2007 =
11:53 AM<BR><B><SPAN style=3D"FONT-WEIGHT: bold">To:</SPAN></B> Joshua =
Goldenhar; dl-Design Review<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">Cc:</SPAN></B> Sandrine Boulanger; Vikas Saini; Manohar =
Divate<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Subject:</SPAN></B> RE: =
snapshot autoremove question</SPAN></FONT></P></DIV>=0A=
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN =
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Hi =
Joshua,</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Please check =
the best practice section in section 8.1 of the =
doc.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb=
sp; </SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">/n/software/FileSystem/snapshot_management_R98_autoremove.doc</SPA=
N></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">Thanks,</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">Henry</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<DIV>=0A=
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =
face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">=0A=
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>=0A=
</SPAN></FONT></DIV>=0A=
<P class=3DMsoNormal><B><FONT face=3DTahoma size=3D2><SPAN =
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">From:</SPAN></FONT></B><FONT face=3DTahoma size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> Joshua Goldenhar =
<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> Friday, =
November 09, 2007 11:35 AM<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">To:</SPAN></B> Jobi Ariyamannil; John Keiffer; dl-Design =
Review<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Cc:</SPAN></B> Sandrine =
Boulanger; Vikas Saini; Manohar Divate<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">Subject:</SPAN></B> RE: snapshot autoremove =
question</SPAN></FONT></P></DIV>=0A=
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN =
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Thanks =
Jobi.</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">These types =
of questions came up in the last design review and were discussed at =
length.</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I think a =
simple rewording of your problem statement can illuminate the overall =
design principle we ended up sticking to:</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">&#8220;</SPAN></FONT><FONT face=3DArial size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">I would like to understand =
why we are willing to possibly delete all of a customer&#8217;s =
snapshots, if they have set and reached their autoremoval high water =
mark (ARHWM).&#8221; <FONT color=3D#333399><SPAN style=3D"COLOR: =
#333399">Becomes:</SPAN></FONT> &#8220;&#8230;why is the customer =
willing to possibly delete all of their snapshots&#8230;&#8221;<FONT =
color=3Dnavy><SPAN style=3D"COLOR: navy"></SPAN></FONT></SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">As Jobi =
mentioned, the customer optionally turns this feature on. It&#8217;s our =
job to make sure the documentation and best practices guides issue this =
warning and make operation as clear and understandable as =
possible.</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">If we come up =
with an arbitrary algorithm to preserve snapshots, there will always be =
a customer that will say &#8220;why did you do it THAT way? &#8211; I =
would rather have had XYZ&#8230;&#8221; </SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I did not =
know we cannot pin the scheduled snapshots &#8211; I imagine we&#8217;ll =
get an RFE in the future to auto-pin snapshots or set a preservation =
threshold on scheduled snapshots. </SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">For now =
though I really feel the simplicity of the feature as implemented makes =
it easy to understand and makes the &#8220;dangers&#8221; easy to =
understand also.</SPAN></FONT></P>=0A=
<DIV>=0A=
<P><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FONT-SIZE: =
10pt; COLOR: navy; FONT-FAMILY: Arial">-Josh</SPAN></FONT><FONT =
color=3Dnavy><SPAN style=3D"COLOR: navy"> </SPAN></FONT></P>=0A=
<P><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FONT-SIZE: =
10pt; COLOR: navy; FONT-FAMILY: Arial">Josh Goldenhar</SPAN></FONT><FONT =
color=3Dnavy><SPAN style=3D"COLOR: navy"> <BR></SPAN></FONT><FONT =
face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FONT-SIZE: 10pt; =
COLOR: navy; FONT-FAMILY: Arial">Phone: 408 963 2408, Cell: 408 547 =
7693</SPAN></FONT><FONT color=3Dnavy><SPAN style=3D"COLOR: navy"> =
</SPAN></FONT></P></DIV>=0A=
<DIV>=0A=
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =
face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">=0A=
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>=0A=
</SPAN></FONT></DIV>=0A=
<P class=3DMsoNormal><B><FONT face=3DTahoma size=3D2><SPAN =
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">From:</SPAN></FONT></B><FONT face=3DTahoma size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> Jobi Ariyamannil =
<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> Friday, =
November 09, 2007 10:13 AM<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">To:</SPAN></B> John Keiffer; dl-Design Review<BR><B><SPAN =
style=3D"FONT-WEIGHT: bold">Cc:</SPAN></B> Sandrine Boulanger; Vikas =
Saini; Manohar Divate<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">Subject:</SPAN></B> RE: snapshot autoremove =
question</SPAN></FONT></P></DIV>=0A=
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN =
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dblue size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">Snapshot auto =
removal is an optional feature somebody needs to turn on.&nbsp; If they =
set the HWM too low, they may end up losing the =
snapshots.</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dblue size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">I don't see =
any need of setting that below 98%.&nbsp; 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.&nbsp; By providing an option for the user =
to specify that threshold, we ended up with all these interesting =
possibilities.</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN =
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dblue size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: =
Arial">Regards,</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dblue size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: =
Arial">Jobi</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN =
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>=0A=
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =
face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">=0A=
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>=0A=
</SPAN></FONT></DIV>=0A=
<P class=3DMsoNormal style=3D"MARGIN-BOTTOM: 12pt"><B><FONT =
face=3DTahoma size=3D2><SPAN style=3D"FONT-WEIGHT: bold; FONT-SIZE: =
10pt; FONT-FAMILY: Tahoma">From:</SPAN></FONT></B><FONT face=3DTahoma =
size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> John =
Keiffer <BR><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> =
Friday, November 09, 2007 10:05 AM<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">To:</SPAN></B> dl-Design Review<BR><B><SPAN style=3D"FONT-WEIGHT: =
bold">Cc:</SPAN></B> Sandrine Boulanger; Vikas Saini; Manohar =
Divate<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Subject:</SPAN></B> =
snapshot autoremove question</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">[opens =
mouth]</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">I would like to understand =
why we are willing to possibly delete all of a customer&#8217;s =
snapshots, if they have set and reached their autoremoval high water =
mark (ARHWM). </SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">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. =
</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal style=3D"MARGIN-LEFT: 0.5in"><FONT face=3DArial =
size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">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.</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">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.<FONT color=3Dnavy><SPAN =
style=3D"COLOR: navy"> </SPAN></FONT>If the last unpinned snapshot needs =
to be deleted in order to free up space, there are bigger issues to deal =
with.<FONT color=3Dnavy><SPAN style=3D"COLOR: =
navy"></SPAN></FONT></SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">[inserts =
foot]</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Thank =
you,</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN =
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">John =
Keiffer</SPAN></FONT></P>=0A=
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN =
style=3D"FONT-SIZE: 12pt"></SPAN></FONT>&nbsp;</P>=0A=
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN =
style=3D"FONT-SIZE: =
12pt"></SPAN></FONT>&nbsp;</P></DIV></DIV></DIV></DIV></BODY></HTML>
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