The Virtualization Room

Mar 22 2007   2:53PM GMT

VMware SAN Guide

Joseph Foran Profile: Joe Foran

Recently posted to the VMware web site is this guide to configuring your SAN for maximum virtualization efficiency (wow, that almost sounded like marketspeak… help me Obi-Wan help me!). It’s an excellent resource on both VMware architecture and SANs in general, containing a copious section on what a makes a SAN a SAN. For anyone who doesn’t know, it’s a Storage Area Network – a way to take a big honkin’ system (or systems) with lots of disks and share them to your servers, which will think they are the same as physically attached disks. The guide goes on to discuss different kinds of SANs and how to configure them to work best with VMware’s various utilities. Failover is also discussed, both from the SAN and the VMware side, as are some aspects of optimization for performance. There is also the obligatory mention of NAS support (NFS 3 only) in VI3, a first for the ESX product line (VMWare used to support it in earlier pre-ESX products, the descendents of GSX/Server).

Most of the reason that VMware published this document can be summed up by this quote from page 130:

“Many of the support requests that VMware receives concern performance optimization for specific applications. VMware has found that a majority of the performance problems are self-inflicted, with problems caused by misconfiguration or less-than-optimal configuration settings for the particular mix of virtual machines, post processors, and applications deployed in the environment.”

I have to admit, that had me laughing. It was the whole “blame the user” mentality that I found funny – I’m glad VMware put the paper out there, but really, they had to expect that the 80/20 rule of troubleshooting would apply to them too – 80% of all problems are human error. The guide does a good job of helping avoid those pitfalls, and goes into detail on setting up your SAN to perform well.

After perusing this document a bit, I’m going to stick with my anti-fibre-channel stance by saying that it’s just not worth the trouble to deploy new FC SANs for a VMware deployment. I’d stick with an iSCSI SAN or NFS NAS if you want the full benefit of shared storage and don’t already own FC SAN gear. Now I have to admit tht I’m biased here… I managed a SAN environment at one point in my career, and I hate Fibre Channel SANs with a passion that rivals how the Red Sox fans and Yankees fans feel about one another (except I don’t think EMC SANs hate me… at least not like human hate anyway, and if they did, I’d have to consider checking into an alternative cognitive function facility, aka the nuthouse).

Another reason I stand against rolling out new FC SANs for VMware is this article by SSV’s News Director Alex Barrett, in which EMC VP Charles Hollis calls for NAS as the best choice for VMware environments. I tend to agree, provided that a number of recommendations, also in the VMware SAN guide, are followed. First among these – forget sharing the storage network with anything else other than VMware. In fact, put it on a completely different set of equipment if you can, just to avoid any processor overhead that VLANing with the same network hardware may incur. It’s gotta be gig, too. That’s in the basic VMware VI3 docs, and repeated in the SAN guide.

The optimization hints consist of a mix of technical and non-technical advice, some of which would generally be overlooked by a SAN admin, and some of which would be overlooked by a VMware admin, such as:

“Choose vmxlsilogic instead of vmxbuslogic as the LSI Logic SCSI driver. The LSI Logic driver provides more SAN-friendly operation and handles SCSI errors better. “

“No more than 16 virtual machines or virtual disks should share the same physical volume.”

“Enable write-caching (at the HBA level or at the disk array controller level)”

There are also equally obvious dummy-errors that are mentioned, things that must happen in real life, but for the life of me seem so stupid that only people who WANT to be fired would do them. My favorite:

“Optimize disk rotational latency for best performance by selecting the highest performance disk drive types, such as FC, and use the same disk drive types within the same RAID set. Do not create RAID sets of mixed disk drives or drives with different spindle speeds.”

This is saying the following – Don’t mix 72gb 10k rpm drives within the same RAID array as 72gb 15k rpm drives. And don’t put a 72gb drive in with 144gb drives. And for pete’s sake, if your SAN supports mixed drive types, don’t ever, ever, EVER mix SAS drives and FC drives. Duh.

As for what this document is not – it is NOT a howto guide to configure VMware many applications in a SAN environment, beyond the direct purview of shared storage. There’s no guide to setting up VMware HA/DRS, though there are several pages dedicated to the storage aspects of these products, including how multipathing your HBAs can affect HA and DRS. Thats left for more product-specific papers, presumably because there’s no reason to be redundant.

Overall, the paper gets 8 pokers.

3  Comments on this Post

 
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  • Joe Foran
    WHo has had a bad experience of doing commercial deals with VMWare?
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  • Joe Foran
    Well its 9.26pm and everyone has been at home for hours, probably snug in the warm cotton land of domestic bliss, as for me... well Im spending my evening in the data center trying to get the best out of our SAN so that datastage can shine on a 64bit Linux virtual platform and Im starting to agree with Jon, its almost impossible to get to that wonderful land of make believe VMware tells us about. Im down to one last issue, reads on the 64bit win 2003 with SQL 2005 are ok , but writes are the issue and not along have the 6 sole beers not inspired any wisdom, but none of the team have any idea what could be causing this issue. All updates, firmware, drivers etc are current, but still the issue remains Withnail
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  • Joe Foran
    Hi! Great! I have just started my participation in a project to design VMWare + DS8000 environment in which we must visualize about 60 Windows 2000 and 2003 32 bit.servers currently running on physical machines. Although I am very experienced with SAN, I have no experience using it with VMWare. That guide saves my life!
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