I can tell you now that OpenSolaris, ZFS & iSCSI is a piece of cake to use and 
work with.  I haven't tested iSCSI with ESX for 9 months or so (I'm looking at 
NFS myself now for ESX), but I seem to remember it worked pretty well and I can 
certainly have another go when I get back to work later next week.

It really is a piece of cake to create iscsi shares with ZFS though, you create 
a new volume and just set shareiscsi to on.  This is an example taken from the 
forums in November 2006! 

# zfs create -V 100M pool/volumes/v1
# zfs set shareiscsi=on pool/volumes/v1
# iscsitadm list target
Target: pool/volumes/v1
iSCSI Name: iqn.1986-03.com.sun:02:4db92521-f5dc-cde4-9cd5-a3f6f567220a
Connections: 0

Note that this isn't a standard ZFS filesystem, you have to use the -V option 
to give you a raw volume to work with.

However, that said, iSCSI is a pain to work with in ESX, the names are 
horrible.  I'm finding that I can get similar performance with NFS, and it's a 
lot easier to just point ESX to a named NFS mount point.  You also have the 
benefit that you can see all your ESX files from Solaris, so backups are a lot 
easier.  If nothing else it's worth doing just so you can use ZFS snapshots to 
take backups of your virtual machines.

Disk controllers are a bit of an issue at the moment, you want to be reading 
through the ZFS forum to see what's written there.  A full blown raid card 
running in pass through mode would probably be my recommendation for the 
controller (since they're designed to handle hardware failures and plain SATA 
controllers may not be).  There's a very good point been raised that ZFS 
guarantees data integrity, data availability is still dependent on your 
hardware and drivers.  Areca are Solaris certified and seem to have a very good 
reputation.

A raid card also has the advantage that you could mirror a couple of devices 
and use that as your slog device.  It does loose a bit of capacity, but gives 
you the benefits of ZFS doing the parity checks for the main pool, while still 
giving you the speed boost from the raid controllers cache.  That will probably 
become academic by Christmas when Sun release their flash hardware to use as 
slog devices, but I think it's your best bet right now, especially if you want 
to get close to your DAS performance since  VMware tends to be heavy on the 
random IO.

Ross
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