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iSCSI drives disconnecting randomly from virtual Server 2008 host

Posted on 2011-09-10
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I have a virtual Windows Server 2008 instance (hosted on Server 2008 using Hyper-V) connecting to a DELL Equallogic SAN via iSCSI. There are 8 iSCSI connections in total, which are then shared as mapped drives on the LAN (40 users) by the virtual Windows Server 2008 instance using Windows shares and login scripts. Once every week or two, some of the iSCSI connections to the SAN will be disconnected (usually overnight) and will not reconnect automatically. When this happens some of the iSCSI connections remain connected. There is no pattern to which connections disconnect and which remain connected, and on the odd occasion all of the connections will disconnect. They can be reconnected manually via the iSCSI connector properties with ease and no errors are reported at any time.

There are no other devices trying to connect to the affected SAN volumes/iSCSI targets and the SAN remains online throughout.

Is there a way of having the iSCSI connections auto-reconnect without a reboot of the iSCSI host? Naturally this doesn't identify the cause, but it would be a useful 'fix'. Any tips on the likely cause of the iSCSI connections being dropped randomly would also be welcomed.

Within the iSCSI properties there is an option for 'automatically restore this connection when the computer starts', which is ticked, however that isn't much use when it comes to random disconnections whilst the server and some of the other iSCSI connections remain online.
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Question by:drl1
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by:5g6tdcv4
ID: 36516077
I would be inclined to look at the "why" not just a temp fix.
is the server connected to the SAN via redundant switches?
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Author Comment

by:drl1
ID: 36516113
Agreed, but a useful fix for auto-reconnecting would also be handy whilst I work on identifying the "why".

The VM host is currently only connected through one switch to the SAN so this may be part of the problem. That raises the question, why would some iSCSI connections drop and others remain connected when they are all connected through the same virtual NIC, physical NIC and switch? Surely if there was a switching issue, then all connections would be dropped and not just some?
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by:5g6tdcv4
ID: 36516121
are you using vlans?
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by:5g6tdcv4
ID: 36516129
also under device manager is "allow the computer to turn off this device to save power" unchecked?
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by:drl1
ID: 36516139
Not using vlans.

I don't see that option in device manager when selecting iSCSI Initiator-->Properties. I expect power settings are not the issue as that would surely disconnect all iSCSI connections and not only some of the 8 connections each time this issue occurs? For example, this morning 3 of the connections had been dropped whereas the other 5 were still connected. Manually reconnecting the 3 affected connections was instantaneous and with no errors.
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by:5g6tdcv4
ID: 36516145
the setting should be on the physical NIC/NIC's in Dev manager
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Author Comment

by:drl1
ID: 36516161
No such setting for the NIC (Virtual Machine Bus Adapter). The VM Host has the correct power settings on the NIC so it cannot be turned off by the OS.
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by:5g6tdcv4
ID: 36516189
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Author Comment

by:drl1
ID: 36516202
That looks like it could be the explanation. I'll read through it more thoroughly when back in the office and will let you know how it goes. Thanks for your guidance so far.
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Accepted Solution

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kevinhsieh earned 2000 total points
ID: 36517497
There is a known issue with Hyper-V where the VM can disconnect under high network load. There is a hotfix for R2 and R2 SP1.

I would make sure that you have the EqualLogic Host Integration Toolkit 3.51 (current version) installed in the VM, and that the VM has two synthetic NICs for iSCSI.  
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