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Line One

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windows software mirroring and SAN

Please note when answering that I am well aware of alternatives to the configuration I am asking about e.g RAID mirroring, etc. but I am not looking for alternatives - depending on the response I get to the specific question I ask here I may post questions exploring alternatives. At this point I only wish to address the specific question I am posting.

Assume I have a Windows 2008 Server and two physically separate SANs that are connected via a separate switch to a 2nd network card on the server - the speed on this SAN LAN is 1 gigabit.  Assume that I have this setup is configured to the point where the drives in the SANs show up in Disk Manager of the server.  With ordinary internal disks at this point I could choose to software mirror the two drives.  Can I do the same with these SAN drives?
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David
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yes
In theory yes you can because Windows will see them as two seperate disks.
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Line One

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Thanks. Have either of you actually done this?
You say network card so I presume you're talking iSCSI.

The Microsoft iSCSI initiator does not support dynamic disks because after reboot you have to go into the iSCSI target configurator and manually attach them, that's going to end up with a broken mirror each time you boot.

You may get away with it using StarPort from Rocket Division instead of using MS initiator, but there isn't a straight yes/no answer to this.
I've just checked this out using freenas as my iSCSI target.  I presented two LUNS to a Windows 2008 R2 and configured them as a software mirror.

I rebooted the 2008 R2 server and the software mirror remains intact with no errors.
Well, unless you can find a definitive statement from Microsoft saying dynamic disks are now supported I'd still say you were taking a gamble, the release notes I can find say "Configuring volumes on iSCSI disks as Dynamic disk volumes using the Microsoft software iSCSI initiator is not currently supported". Admittedly that's for 2003 but in that case I would expect some MS documentation saying that dynamic disks on iSCSI are supported on 2008, be interested if anyone can find such a statement.
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jakethecatuk
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Oh, well found. I must have been looking at an old version of the release notes. In that case I agree it'll work (although it's much better to mirror the SAN boxes themselves if possible).
jakethecatuk:

Excellent. Thanks for the extra legwork.