A new SAN – good idea for us? [closed]

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Question :

I work for a small non-profit organization which has 2 infrastructure administrators. They have experience with Windows server administration and virtualization, but no experience with SANs or SQL Server. I serve as the only SQL Server developer and SQL Server administrator. Recently, the infrastructure administrators told me they were looking to purchase a SAN and store in it all of the SQL Server data files. I expressed concern that neither of them had experience administering a SAN. They responded by telling me that modern SAN hardware has drastically simplified SAN administration (probably a point made by Dell). Unfortunately, I’m not in a position to say with authority that their decision needs more consideration. I am concerned though that they are about to bring in a component (i.e. the SAN) that could add significant risk and performance implications because they don’t have the experience to properly administer it. Am I wrong? What are your thoughts? Can you give me some advice?


Answer :

A SAN isn’t something to be nervous about. Yes, there a bunch of capabilities (software) that come with it which enable features like replication and auto-tiering, but those are above and beyond the basic performance. At the end of the day they’re still a bunch of disks behind controllers designed to optimise availability and performance.

There are a number of “degrees” of SAN, from the basic shared disk arrays accessible over iSCSI or Fibre Channel to the big boys like EMC etc. and the SAN appliances using pure SSD. As you are a not for profit I’m guessing that this is probably towards the lower end of the spectrum in terms of price.

The questions I would ask are “What benefit is there to this for the databases?” and “Who will be responsible for administering this?” (I guess the infrastructure admins)

Ultimately, ask that a contingency be put into the budget to hire a consultant from the SAN provider to help with configuration in the event that the performance isn’t what is expected.

There are a lots of questions I’d like to ask to give you a more definitive answer (How many servers do you have? What kind/speed of disks are you running locally? What do your current IO loads look like? etc), but at the end of the day, a great many organizations are using SAN’s to store database files.

SAN technology is something I would recommend getting familiar with, if only understanding what you need to test with it and why. Local disk is risky since if that disk fails, you’ll need to replace it before you can restore your latest backup unless you have spare hardware or a failover box to use.
SAN’s are good for businesses as they help mitigate that risk by spreading that database file across 15 disks so if one fails, you’re not down until you can replace the hardware (in most cases, I’m no SAN admin).

Your concerns are valid, but I’d give your sysadmins the chance to alleviate your concerns. Approach them with metrics around your current IO loads and how your instances are built and get them to either explain or get the vendor to explain what you need to hear to feel comfortable. If you get railroaded despite your concerns, then you did you part and addressed the issues you had.

If you’re still nervous – reach out to the SAN vendor you’re considering. You’d be surprised how much they’re willing to help, especially if you’re a prospective customer.

Always be open to helping the business move forward, even if that means making something work you’re not entirely comfortable with. Express your concerns, have metrics to back it all up, and if they move forward despite evidence, do your best to keep it operational and performing.

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