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Netapp 3140: Why did the volume go offline?

The volume containing our exchange LUN went offline today.  A consultant brought it back online and remounted the LUN.  But he said he did not know what caused the Volume to go offline.  How would one approach finding the root cause of this?  Thank you.
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Paul Solovyovsky
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There are several reasons the LUN can go offline, most of the time this is caused by:

1. Volume in the OS running out of space - Evident in OS
2. LUN is fragmented and due to fragmentation runs of out of space on Netapp volume
3. LUN and snapshots run make run out of space on Netapp volume  

There should be logs one why this happened, if the consultant can't figure out you may want to seek additional help.

For item #2 run space reclamation from Snapdrive.  As the Netapp LUN is actually a file inside of a Netapp volume (hence the "filer" terminology) it may get fragmented especially if you're running sql/exchange logs or backups that get added and deleted frequently.

For #3 Review your snapshots and and storage used on the Netapp volume.

What type of data is on this volume? Are you using snapdrive?
Also run a quick check

in CLI run "rdfile /etc/messages" if happened recently, otherwise it may be messages.0, messages.1 file.  This should have the error that caused it dismount
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Looks like I asked this before getting the full story from the engineer who fixed this.  What happened was that the LUNs disappeared from the Exchange server.  So he took the volumes offline and then put them back online.  Then he went into the Exchange server and remapped the LUN.  So seems more like a snap drive problem or something like that.  There were some errors evidently in Windows complaining about "signature"?  There was enough space at the LUN and Volume levels.  Any thought on why drives might disappear from a Windows VM causing Exchange to lose access to its database?  Thank you both for the pieces you've already contributed.  I am sure I will use that too.
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Paul Solovyovsky
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A snapshot issue is a distinct possibility.  At 04:31 there was a snap shot deletion.  And the LUNs went offline at 04:33.  Now there have been many successful automated snapshot deletions prior to this.  So that time association could just be coincidence.  We use iSCSI.  Will run thought your other suggestions.  Thanks again Paul.  You rock.