Its been a while since I wrote something, so I feel obligated to make a post geek related. A few months back I started looking into a way to offer some sort of high availability to our sites while decreasing the cost. Previously we would cluster up the SQL server and hope for the best. Obviously this is not great, and still quite expensive to only have 2 servers with any level of redundancy.
When I started looking at shared storage and VMWare solutions, I came into the same issues. There are not many choices in the realm shared storage that is fast and offers redundancy without using multiple units. That is when I started looking at the VSA software. If you have not seen this before, it is pretty cool. Essentially you take the DAS disk from multiple ESX servers and create RAID sets across the servers.
This presents a few pros and cons depending on how you design this, and what you are going to use it for. If you use at least 3 servers and RAID 10 sets to provision your LUNs, then you can lose one of your 3 ESX hosts and you will stay running. With vMotion from VMWare, any servers on that host will fire back up on one of the other hosts. You need to be careful that there are enough resources to lose 1 server. Another positive to this design is that you are able to expand out by adding disk shelves, additional servers, or even moving to an HP SAN later (like a p2000). Expanding out more disk, or moving storage around is simple with the VSA interface. Very impressed so far.
There is a downside to all of this. There is a ton of disk overhead to contend with. You do have choices, but the most popular appears to be RAID 5 sets for the raw disk, and then RAID 10 on top of that. Its pretty obvious that this will slow things down a little bit when it comes to disk. You can combat this by using fast disk, but there is only so much you can do. If you are using very high I/O applications, I would not recommend this solution.
We are lucky that the applications we use for our remote sites do not have really high disk I/O. This solution allows us to offer highly available applications and makes it easy to expand as their needs change.