SAN disk configuration

  • I am in the process of configuring a new SAN for a SQL Server. I am going to use RAID 10 for all raid groups. I have enough drives to do the following:

    Tempdb - 4 drive Raid 10

    Logs - 4 drive Raid 10

    Data – 12 drive Raid 10 (will contain the following files:

    primary data file – 46% of all the IO on server

    secondary file that contains all of the indexes – 33% of all the IO on server)

    My question is, should I put the data and index file on the raid group with 12 drives or should I split up the 12 drives to make a 8 drive Raid 10 raid group for Data and 4 drive Raid 10 raid group for the Index file. Would it be better to have a majority of the IO on a 12 drive group(lots of spindles) or split it up the IO into two different raid groups so they don’t compete against each other.

    I appreciate your input.

  • Personally, if you're going to go through the effort of maintaining separate file groups, you need the separate physical spindles to get the true benefit from them for optimization. I would go with 8/4.

    I'm not sure if two spindles alone (Raid 10, cut your spindle count in half) are worth separating like that though from a speed perspective. It might be worth RAID 5'ing that 4 spindle with the indexes for a higher spindle count, but that will depend on data volitility.

    And if you can, as annoying as it is to setup, go RAID 0-1 (striped mirrors) instead of 10 (a mirrored stripe). You have a better chance of surviving a dual drive failure that way.


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