EqualLogic invited themselves in to our conference room yesterday to show us one of their iSCSI SAN arrays. All I can say is...wow. If you're looking at a SAN solution, definitely consider EqualLogic. And they will jump at the chance to give you a 2-hour in-house demo.
But regarding my post the other day...boy was I way off. Apparently I didn't understand storage virtualization. I was debating how to split the drives up, half RAID 5, half RAID 10, or all of it RAID 10...
EqualLogic introduced me to RAID 50. It requires a minimum of 6 drives not including a spare, so I'm not surprised I never came across it before. It basically takes 2 RAID 5 sets and stripes between them (RAID 0).
The EqualLogic PS3900XV has 16 300 GB drives. 2 RAID 5 sets is 8+8. A spare on each leaves us with 7+7. And the parity bit brings us down to 6+6. So out of the 16 drives, we get to use about 12 of them space-wise, at least 3.4 TB. EqualLogic also reserves some space on each drive for housekeeping, but this shouldn't end up being more than 200 gig or so (the tech couldn't remember if it was 20 megs or 20 gigs reserved per drive).
RAID 5 would have given us 4.5 TB but would have been pretty slow on write speed. And RAID 10 would have given us 2.4 TB. So 3.4 is pretty good...
And even better is the fact that its all virtual. We make a LUN for our file server, one for Exchange, one for SQL, etc. But we can grow these LUNs at any time, so instead of saying the file server gets 2 TB and Exchange gets 600 GB, we can just set them to about 150% of what they are right now and then expand them as they need it.
My only question now, and one that EqualLogic couldn't answer for me, was do we put all of our system drive VMDKs on a single LUN or make a seperate LUN for each server? I've posted a question on the VMware forums, and I'm sure a lot of people thought about the same thing while setting up VI3 and a SAN.
Friday, September 14, 2007
EqualLogic wants to sell us stuff
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You may also want to take a look at LeftHand Networks. They have all the features that EqualLogic has plus more. Not only do they virtualize within a box, but across boxes. LeftHand's Network RAID stripes and replicates data so that a cluster of arrays can accommodate a double disk fault (second drive in a RAID set failing while rebuilding a failed drive using a spare), a complete array failure, or a site failure. This comes in handy when using VMware VMotion and HA. These VMware capabilities require that the underlying storage is still in tact when failing over or moving a VM. With LeftHand, a site can be brought down, the VMs failover seamlessly and the SAN is still available. My understanding is that LeftHand is the only one that can do this over IP.
If you have servers with storage in them, and you don't have budget to by a SAN from LeftHand, you can take a version of their software that's shipped with their SANs and run it in a VM on each server (called VSA), and it pools all disks from your servers into a shared SAN, and it looks and is managed just like an external SAN.
LeftHand has definitely taken storage virtualization to the next level. You can download a fully featured trial version of VSA from their web site for free. It's a good way to evaluate LeftHand's capabilities without having to install and configure hardware.
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