C: Drive Cluster Size of 512

Discussion in 'Server Setup' started by James B, Dec 4, 2008.

  1. James B

    James B Guest

    I just discovered that the C: drive (the primary partition) of our server
    has a cluster size of 512 instead of 4k. How much of a performance issue is
    this and should I change the cluster size to 4k?

    We're running SBS 2003 R2 on a Dell server. We used the Dell server
    install CD's to setup the system and never noticed that it had formatted the
    C: drive with the 512 cluster size.

    If changing the cluster size is important, what utility would be best?
    Obviously I'd prefer to convert the drive without having to reload the OS if
    I can. I can take the server down and hook its c: drive up to a workstation
    if converting the active/primary partition is an issue.

    James B
    James B, Dec 4, 2008
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  2. Hi,
    you should be aware , that encryption is not possible on all cluster sizes.
    Juergen Kluth, Dec 4, 2008
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  3. James B

    James B Guest

    Thanks for the tip. We're not using encryption on the system partition.

    James B
    James B, Dec 4, 2008
  4. It can have a considerable negative impact on disk performance.
    Depending on your average file size, there can be a lot more disk I/O's
    involved in handling 512 byte clusters than there is in handling 4K
    clusters. It can also have a negative impact on disk fragmentation, it
    takes 8 - 512 byte clusters to hold what one 4K cluster can hold, these
    7 extra clusters can cause considerably more file fragmentation and this
    in turn can lead to performance degradation. If most of your files are
    512 bytes or smaller then the smaller clusters would be efficient at
    using disk space without affecting performance but with larger files
    disk space efficiency usually takes a back seat to disk I/O performance.
    With 512 byte clusters you might find that your disk does a lot of

    I may be overly cautious, or plain paranoid, but when it comes to NTFS
    formating, conversion or cluster resizing I simply do not trust any
    third party utilities to do the job. I'm sure that others will disagree
    with me and that they will make solid suggestions based on their experience.

    John John (MVP), Dec 5, 2008
  5. James B

    James B Guest

    Thanks for the info (and for confirming my suspicions). I've been trying
    to figure out why my server seems like it's dragging even though it has 2
    quad-core 2.66 Xeons on a 1333 bus. The fragmentation was pretty bad -
    especially considering that we only have the OS & programs on the C: drive
    and have all other data & exchange DB's on a separate drive.

    Thanks again,
    James B
    James B, Dec 5, 2008
  6. You're welcome. Installing Windows almost always leaves the disk in a
    pretty badly fragmented state but when you do a bit of math the problem
    of excessive fragmentation with smaller clusters becomes quite evident.
    For example, it takes 128 - 512 byte clusters to hold a 64K file
    compared to 16 - 4K clusters.

    John John (MVP), Dec 5, 2008
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