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iSCSI SAN Questions

Hi guys,
I have some questions about iSCSI SANs that I'm hoping someone can help me with.

I want to deploy a FreeNAS iSCSI SAN (sort of anyway) and I'm wondering if I can use a standard Gigabit switch for this. I mean to use a couple of gigabit NICs teamed for greater throughput and I have a few spare 8 port gigabit switches which I could dedicate to this lab, but I'm wondering if this would work or if there would be pitfalls to this setup. Is there anything obvious I have missed, or "should" it work?

Also, is it possible to point several initiators at a single LUN on a target? I ask because this seems to be the basis on which vMotion works, but I thought it was not possible to connect a single LUN to multiple initiators. Any pointers to good reading material would be very much appreciated, as would any real life experiences or examples.

Thanks for any help you can give.

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Permalink Reply by Jeff Hengesbach on January 6, 2011 at 6:27pm

Stefan,

The short answer about the 8 port switches is - sure. iSCSI can go over any network gear. In a lab situation the quality of the switching gear may not be an issue -if the similarity of your lab doesn't have to match your production environment. For high demands / production be sure to look into quality, full line rate switching gear.

You can absolutely have multiple initiators access the same Lun/Target - if the filesystem on the LUN supports it. VMware uses VMFS which is designed to have multiple system access it simultaneously. You could not for example point several Windows systems at an NTFS Lun without running into trouble.

It sounds like you are just getting into playing around with VMware. There are literally thousands of websites out there about VMware, storage design, iSCSI, etc. Let Google be your friend ;)

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Permalink Reply by Stefan Pynappels on January 6, 2011 at 6:38pm

Hi Jeff,

Thanks for that reply, it makes sense about having several Initiators accessing the same LUN if the FS allows it, every time I have seen it referred to as a problem has actually been on NTFS drives.

Good news on the switches working too, means I don't have to spend more money to extend my lab. I have several ESXi hosts running, but to date I have used internal datastores on them so have never looked into iSCSI in any great depth before.

Great fun learning though, I'll let you know how I get on.

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Permalink Reply by Stefan Pynappels on January 10, 2011 at 9:32pm

Ok, I ditched FreeNAS and went for Openfiler. Bit of a pain to set up to run from a USB stick, but worth it. Joined my second ESXi host to it and have VMs on both boxes running from it.

Sweet!

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Permalink Reply by Paul Stoklosa on January 11, 2011 at 4:01am

A gig switch is a gig switch if that's all you need.. Should be fine.. But beware.. Openfiler is nice.. but I don't believe it supports the 'reservation' required to share a volume between multiple hosts. This is needed for things such as vmware vmotion, and windows/SQL clustering (which is what i was testing when i discovered the limitation.) There is an alternative I found that works nicely with Windows/SQL clustering (haven't tested VMware).. Comstar on Solaris. I posted some short notes on this on http://sysadminx.wordpress.com/2010/10/26/test-san-functionality-wi..., but I'm sure a google search on the 2 terms will give you tons of leads..

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Permalink Reply by Stefan Pynappels on January 13, 2011 at 10:45am

I've heard that about Openfiler before, but I have 2 ESXi hosts accessing the same VMFS LUN on the Openfiler Server and both have VMs stored on it and running correctly. Not sure about vMotion etc, as I don't have a vSphere license.

I'm using a couple of cheap unmanaged Gigabit switches, so Jumbo frames are a little pie in the sky at the moment, but performance is fine just the same. I don't have anything really intensive running on it though, but still, as a test, I'm happy.

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Permalink Reply by Paul Stoklosa on January 11, 2011 at 4:04am

oh.. and if the switch supports it, try turning on jumbo frames for each device from end to end for better performance. And if you want to emulate a production system, use 2 nics in each server, and 2 gigabit switches, connected to 2 ports or nics on the target to avoid a single point of failure. Overkill for a test environment, but a must for really critical systems.