SAN Disk Fragmentation & SQL Server

Posted on 2006-05-08
Last Modified: 2013-11-15

MS SQL 2000 Index Defragementation Best Practices article, states that  "On scale environments that benefit from more intelligent disk subsystems, such as SAN environments, corercting disk fragmentation is not necessary"

Is this actually the case or will a heavily fragmented SAN have a performance impact on SQL.


Question by:ShogunWade
    LVL 15

    Accepted Solution

    Hi ShogunWade,

    I understood this to be correct since hotspot activity gets balanaced out in intelligent SANs.  As I understand it ('course I may be worng!) in big SAN's you don't really have a "disk" - you have virtual space where things are stored, depending on how the SAN feels it may move the data around in order to spread load away from busier disks and onto quieter ones.  Fragmentation becomes less of an issues because of the large number of disk spindles you have accessing your data in parallell.  I think that by defragmenting you a try a pile everything together which negates the point of spreading the load through the SAN.

    So I think it is actually the case.
    LVL 18

    Author Comment

    Thanks for the feedback mc,   this sounds very plausable.   Im keen to leave the question open for a short period if you dont mind just incase someone has any info to the contrary, but what you say sounds fairly robust.

    LVL 15

    Expert Comment

    ...however - rereading your question (I was really only thinking in terms of physical disk) and looking over the article ( )?  I think the statement above only relates to physical disk defragmentation, the following suggests that SQL index defragmentation is still a worthwhile activity, I guess that the bigger the SAN the quicker it would occur as well.

    "Obviously, having a high-performance I/O subsystem benefits SQL Server performance; however, performance gains can still be realized by defragmenting indexes across all systems."
    LVL 18

    Author Comment

    Cheers once again MC.

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