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For anyone else's benefit, I received the following from somebody at Dell/Equallogic support directly via e-mail:
I saw your post on the Oracle Forum, so I thought I would take a stab at answering it.
What OS/version is OVM 2.2.2 based on?
You do not have to use the HIT/LE software to add another member. The HIT kits do provide optimal performance in multimember pools, When they are not available, for every iscsi session from the initiator, an additional connection is made to any other members having data for that volume. EQL calls that a "MESH" connection. The arrays can move this data between members very efficiently, especially when jumbo frames are available to the array ports. As you add more and more members to that pool, volumes typically only stripe across three members. Unless it's too large to fit. So at two members you should have no problems until HIT/LE is available for OVMS. I don't know when that support will come, Oracle is on the list to get certified.
The HIT kits for Linux and ESX are relatively new. So our customers have been using them w/o a problem for quite sometime. Not all ESX customers have the required license in order to use MEM for ESX.
re: OVMS kernel well according to uname -a, OVMS 2.2 uses 2.6.18-188.8.131.52.28 which is their kernel but that puts it in the general 5.2 area. I don't know what other patches they roll into their distro.
My reply to him is:
Thanks very much. I was not aware of the mesh. I was told that if we didn't use the HIT kit, then the iSCSI connection would go to one target. If the block was on a different member, then the member with the connection would get the block on the host's behalf and then return it, causing four network packets instead of two: (host)->(member 1)->(member 2)->(member 1)->(host). Not great for performance.
How does multipath know where to send the request when a volume is split without your dm-switch kernel module?
As for OVM, I don't really know either. They don't release the information. However, what I glean from the web is that almost all of the changes are Xen-related and have very little to do with the rest of the kernel. It is an issue that they are so far back, but they did release OVM 3.0 recently which must be a newer kernel. It is also a MAJOR change, since they rolled in some of their Virtual Iron acquisition. We are very afraid to upgrade! ;-)
So, one thing at a time. First we need to get the new EQL box into the mix and get everything stabilized. Then we can look at OVM 3.0. Oracle has their Storage Connect initiative which is supposed to make all of this transparent, but Dell/Equallogic hasn't announced support yet. :-/ Hope springs eternal...