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Virtualise your servers: storage strategy

Posted on 5 Jan 2010 at 14:41

Jon Honeyball considers storage in the final part of his guide to virtualising your servers

I now propose to look at a completely different way of using iSCSI storage for VMs. To cover the hardware first, I’ve bought a pair of Iomega StorCenter Pro ix4-200r NAS servers, one is the 2TB version and the other a 4TB version – they cost about £1,000 for the smaller and £1,500 for the larger. Both are four-disk units arranged as RAID5, so I get about 2.7TB of usable space on the larger one and 1.3TB on the smaller.

RAID5 protects against the failure of a single drive in each array, and both boxes are intelligent enough to email me and tell me something has gone wrong.

On the 4TB unit I can build my own disk partitions and present them using iSCSI onto the network wire. These devices do CIFS, SMB, Apple File System, FTP and a host of other protocols too, but let’s skip over those for now. For this project I’m going to create a bootable volume on the machine in which the entire virtual server is stored, so all the storage is wrapped up into a partition held on the SAN, but the VM actually runs on the processor and RAM of another box that’s the host server.

RAID5 protects against the failure of a single drive in each array, and both boxes are intelligent enough to email me and tell me something has gone wrong

Why do this? Well, if you want to move a running VM from one host to another it’s going to be much quicker if you don’t have to move tens of gigabytes of VM data storage: just move that virtual machine’s memory image, processor set and so on to the new box, then redirect the remote storage to the new location and it can be back up and running far faster.

Similarly, you could keep the VM running on your chosen host, but swing the storage from one SAN box to another. Maybe you need to shuffle things around because you’re running out of space on the first SAN box, so move the entire storage of one VM to another box with a few mouse clicks. Want to move a VM both ways at once? Move its host to another host box and move its entire VM storage to a different box. The choice is now yours.

There are alternatives. For example, you can run a VMware engine, which makes your local disks look like a SAN. After all, that’s all the processing engine does within the SAN boxes themselves. Companies that offer this sort of functionality include LeftHand Software – now part of HP – so I could have stuffed my servers with disk space, installed the LeftHand software, and then presented the locally attached disk as if it were a network-attached iSCSI SAN.

Getting an iSCSI SAN running is a hoot, and a great learning experience

Then there are still other companies that can suck up all the available disk space on all your machines and present it as one integrated SAN, but this is something for later on in the series. For the time being, getting an iSCSI SAN running is a hoot, and a great learning experience, and I highly recommend it to give you centralised storage management, backup and DR.

You might be wondering why I bought two boxes from Iomega. To be honest, Iomega was one of those brands that I preferred to keep at arm’s length (preferably with the hand holding a pointy stick) since its click-of-death disasters of a decade ago. I know it isn’t fair, but mud sticks.

However, EMC bought Iomega more than a year ago, and EMC owns VMware. And take a look – these new “Iomega” boxes are really EMC boxes in disguise, and right there on the hardware-compatibility list for VMware vSphere 4. Quelle surprise! And so far I’d have to say I’m very impressed with them

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