Give your SAN to the SQL Team, Part #2
Exchange 2010 introduces the concept of Database Availability Groups, or DAG for short. It’s a High Availability model that uses the best bits from Exchange 2007, known then as CCR, and uses the same technology to ship the database logs to as many members of the DAG as you may have configured. Since you’re shipping logs around and NOT the database as you did previously with your replicated SAN that means that now each copy of the database on each of the DAG members is a clean copy of the live database.
In Part 1 of this series, we made the audacious claim that you could use SATA disks without RAID to run Exchange! Here's how you can achieve it.
If any of the copies of the database has a minor glitch because the disks you’re using develops a bad sector, then each server is able to reach out to any other copy and request the page which has corrupted and receive a known good clean copy to patch itself with automatically.
Does that mean that Exchange can’t use SAN’s anymore? Of course it doesn’t. Exchange 2010 is able to use virtually any kind of disk you allocate to it. SAN volumes, DAS (Direct Attached Storage) shelves or JBOD (Just a Bunch Of Disks). Irrespective of the disk you give Exchange, you’re able to build a highly available distributed unit of high availability.
Using lots of relatively cheap and large SATA disks means you’re able to deploy lots of cheap Exchange servers with large mailboxes, which are highly available and mostly self-repairing. Using your SAN means you’re provisioning finitely sized mailboxes and expensive storage which is now potentially overrated for the task required. As you may know, redundancy in your SAN isn’t cheap either, and mirroring your SAN to an offsite location can be desperately expensive. In short, the use of SATA allows high availability to be achieved by distributing Exchange databases across cheap storage as opposed to one massive SAN which is mirrored somewhere else.
CAN Exchange benefit from your SAN? Of course it can, but you may find that the performance you get using low cost SATA based storage option with Exchange built in high availability through DAG’s will service your organization better than your SAN will. In fact, if you hand your high cost SAN back to your SQL teams for their use and step away from SAN infrastructure for your email, your company will win on two counts and you will become a hero outside of your own team!