Disk I/O for Exchange 2010

Posted on 2011-10-06
Last Modified: 2012-05-12
I am looking at creating a disaster recovery site for my Exchange 2010 implementation.  The issue that I am running into is picking out a RAID that will be able to handle the I/O from Exchange 2010.  What is the best way to determine how much I/O is being generated by my current system?  I have a couple of different arrays that I am looking at and the only real difference that I am seeing between is cost and I/O capability.  I want to make sure that I am picking the correct system to handle the I/O.  I know in UNIX I would run iostat –xtc 15 > /tmp/io.txt and looking at the information in there, but there are a lot more options in Windows 2008 Enterprise Edition SP2 for disk I/O.  Which counter/counters are going to provide me the best information?
Question by:warewols
    LVL 46

    Expert Comment

    Windows' performance monitor does a good job reporting how much I/O goes on at the LOGICAL level, but if you want to see physical disk I/O, then you need to get something that can drill into your specific raid controller.

    Author Comment

    Any specific counters that you recommend looking at on perfmon?
    LVL 46

    Accepted Solution

    The biggest one you care about is queue depth.  If it is always in the 0-2 range, then bottleneck isn't disk I/O, it is elsewhere.  It will report read and write MB/sec, but those numbers are really a bit fuzzy as they represent what the programs are asking the RAID to provide, and not necessarily accurate enough to make a decision for whatever you are trying to do.  Filesystem settings, load balancing, and other factors can skew the results.

    Example,  on RAID1, some controllers do load balancing.  In perfect world, 50% of the reads get serviced by each disk, whatever disk can get to the data fastest, or has it in cache.  Not all controllers do this.   Windows has no idea what is going on.

    If you bench, make sure you bench and do data integrity testing and degraded performance.  EVERYTHING is easy and works when hardware is healthy, but what happens when you are doing a file system defrag and you yank out a drive in the middle of it?  Does I/O hang for 1, 2, .. or 60 seconds?  Does performance drop by 10% or by 90%?


    Author Comment

    Performance is fine for the current Exchange 2010 production system.  I am just attempting to spec out a brand new system for a disaster recovery site.  I would like to know what my current I/O is so that I can spec out a disk array for the new system.

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