Sunday, 14 January 2007

more about iSCSI

I mentioned as a "Storage Resolution" to look more in-depth at iSCSI. Well I've started doing just that today.

The first thing I thought I needed was a working environment. I'm not keen on investing in an entire storage array (at this stage) to do the testing (unless some *very* generous vendor out there wants to let me "loan" one) so I've build a virtual environment based on a number of free components.

I've a dedicated VMware testing machine recently built which has a dual Core Intel processor, 2GB of RAM and a SATA drive. Nice and simple. It runs Win2K3 with the free VMware server, onto which I've created another Win2K3 R2 partition and a Linux partition running Fedora Core 6. This is where my iSCSI "target" will sit.

For those unfamiliar with SCSI terminology, the source disk or disk system presents LUNs which are referred to as targets. The host accessing those LUNs is the initiator; simply put the host initiates a connection to a target device, hence the names. My iSCSI target in this instance is a copy of the Netapp simulator running on Linux.

Most people are probably aware of the simulator. If not, Dave Hitz talks about it here. I've created a number of disks into an OnTAP volume and out of that created a LUN. LUNs can be presented out as FC or iSCSI, in this instance I've presented it out as iSCSI.

By default the simulator doesn't enable iSCSI so I enabled it with the standard settings. This means my target's iSCSI address is all based on Netapp defaults. I'm going to work on what the best practices should be for these settings over the coming days. Anyway, I've presented 2 LUNs and numbered them LUN 4 and LUN 9.

At the initiator (host) end, I've used my Win2K3 Server and installed the iSCSI initiator software from Microsoft. This gave me a desktop icon to configure the settings. Again, I've ended up with the default names for my iSCSI initiator, but that doesn't matter; all I had to do was specify in the iSCSI initiator settings the IP address of my target, log on and it finds the LUNs (oh, one small point, I had to authorise the initiator on the simulator). Voila, I now have 2 disks configured to my Windows host which can be formatted as standard LUNs.

As a performance test, I ran HdTach against the iSCSI LUNs on Win2k3. I got a respectable 45MB/s throughput, which isn't bad bearing in mind this environment is all virtual on the same physical machine.

All the above sounds a bit complicated, so I'll break it down over the coming days as to what I had to do; I'll also explain the iSCSI settings I needed to make and my experiments with dual pathing and taking the iSCSI devices away from Windows in mid-operation.

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