topic Re: MSA2012i ISCSI in Disk Enclosures

MSA2012i ISCSI

motech2 — Fri, 17 Apr 2009 14:52:54 GMT

Hi, I am looking at configuring some luns on a new MSA2012i. It will be used for ISCSI luns holding VMWare servers running from ESX hosts.

My first question is whether, given that I want to have multiple virtual servers hosted on the MSA, accessible from multiple ESX servers (clustering / failover etc) should create one huge LUN that I could hold multiple VMs on and make accessible to all my ESX servers or whether I should carve the storage up - what's the pro's and con's?

My second question is really performance wise - what raid level should I use? I will have a range of things being hosted - from very fast IO SQL to low IO boxes just serving up some files. They're 15k 300GB disks and I can have lots of them if I need them.

Any thoughts much appreciated.

Re: MSA2012i ISCSI

Uwe Zessin — Fri, 17 Apr 2009 16:22:26 GMT

Is this a 2-controller MSA2012i? If yes, then I would create at least 2 MSA volumes which can be split across both controllers. Well, I would do that anyway in case you upgrade later.

Unfortunately, here is no single correct value for a VMFS volumes. I have customers with as small as 150GB (many small VMs) and others with up to 800, 900 or 1000GB (database servers) volumes.

Remember that there is one I/O queue to each VMFS volume and more volumes = more I/O queues. On the other hand: many volumes = much scattered free space. The choice is your's ;-)

Even if you create multiple volumes, I suggest to present them to all ESX servers. Unlike file systems like NTFS or EXT2/3, the VMFS can deal with multiple readers/writers without a problem.
That enables you to use other ESX features like VMotion(and DRS), HA and Storage VMotion.

Re: MSA2012i ISCSI

motech2 — Fri, 17 Apr 2009 16:29:37 GMT

That's helpful thanks. Yes it's dual controller.

So Multiple volumes to be spread between controllers makes sense. Is this controller assignment done at the vraid level or at volume within vraid disk setup?

IO queues are important. On the basis that someone might execute a big table scan on an SQL volume I wouldn't want the IO queue affecting everything else. In this scenario I guess I'd have to have the VMFS containing the SQL data in it's own volume with an IO queue, and other data in it's own volume. Am I correct?

Also I keep reading that ESX only supports the ISCSI for msa2012i at software level. Has that improved recently?

Re: MSA2012i ISCSI

Uwe Zessin — Fri, 17 Apr 2009 16:51:07 GMT

The controller ownership is at the 'virtual disk' (vdisk) level. A vdisk is a RAID container which provides space for one or more 'volumes'. A 'volume' is then presented to one or more hosts (servers) and provides a disk space.

If you want to hard-partition your I/O, yes, create a separate vdisk with a volume onto which you create a single VMFS datastore which is used for one virtual machine. That's an extreme, but if you absolutely need, it is possible.

I have not checked, but you could also install an iSCSI sw initiator into the Linux/Windows guest to offload the VMkernel iSCSI initiator. I am not very familiar with the latest features of the Linux version, but the Microsoft one has been offering features like path failover and even load balancing for years (in 2007 I ran some tests and was able to read up to 180 MBytes/sec across two Gigabit links from another vendor's array into a ESX servers' Windows VM).

Last year I've set up a small ESX cluster with an MSA2012i. During setup I ran some tests from a Windows 2003 VM via the VMkernel software iSCSI initiator against a single 3 or 4 member RAID-5 vdisk/volume on 300GB/15kRPM SAS disk drives. With IOMETER and some unrealistic 'benchmark'-parameters I was able to get 100+ MBytes/sec reads and 50-70 MBytes/sec writes.

Re: MSA2012i ISCSI

motech2 — Fri, 17 Apr 2009 17:05:00 GMT

Again that is really useful - thanks for your help.

One last thing - in the setup it talks about having each IP address in a different subnet. Why is this? Is there some sort of arping issue when controller failover happens? Different subnets seems a bit extreme.

Re: MSA2012i ISCSI

WilliamReed — Sat, 18 Apr 2009 03:34:36 GMT

Dont use ISCSI for VMs. It is initiated at the software level and can be slow. We are switching out our 2 node 6 VM per server with a MSA2312fc.