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How identical is a disk mirror? - Sun Solaris

I've mirrored a boot disk with an geometrically identical drive, using the Solaris Volume Manager (Disksuite) on Solaris 9 x86. What can I expect if I switch the two disks while the power is off, and then boot the system? If the mirror is really identical, then there should be no difference in system behavior. Is this true, and is this risky? Regards, Michael...

  1. #1

    Default How identical is a disk mirror?

    I've mirrored a boot disk with an geometrically identical drive, using the
    Solaris Volume Manager (Disksuite) on Solaris 9 x86. What can I expect if I
    switch the two disks while the power is off, and then boot the system?

    If the mirror is really identical, then there should be no difference in
    system behavior. Is this true, and is this risky?

    Regards,
    Michael
    mschloh@netscape.net Guest

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    Darren Guest
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    Andrew Guest
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  4. #4

    Default Re: How identical is a disk mirror?

    In comp.unix.solaris net wrote: 

    The short answer is "It depends, and yes, it is risky".

    Depending on the version of Disksuite/SVM you're using, and the type
    of disks (eg, SCSI, FC-AL, IDE) it's possible for SDS to get very
    confused when you do this.

    It will most likely appear to work at the time, but at a later stage you
    can get things going wrong. eg, with some versions of SDS and FC-AL disks
    doing that can result in SDS offlineing the wrong mirror when an error
    occurs at a later stage. ie, if you get an error on one side of a mirror,
    Disksuite can offline the other side of the mirror!

    I believe this particular problem has been has been fixed in later
    version/patches, but I'm not certain...

    Scott.
    Scott Guest

  5. #5

    Default Re: How identical is a disk mirror?

    net wrote: 

    The drives are only identical from point that the LVM takes over.

    That is to say their partition tables should be identical, their LVM private
    areas should be identical, their LVM public areas should be identical, the
    logical volumes living in the public area should be identical. The data in
    the filesystems in those logical volume will be identical to the ability to
    flush all changes from system buffers.

    But that isn't everything on the disk.

    The first few blocks are the boot block. It's outside of the rest.
    "installboot" puts the boot block there. This applies to SCSI drives,
    so if there's an "installboot" on your X86 machine it will do what you
    need. Otherwise the first few blocks are the MBR. It's outside the
    rest. "Program X" puts an MBR in place ...
    Doug Guest

  6. #6

    Default Re: How identical is a disk mirror?


    "Andrew Gabriel" <demon.co.uk> schrieb im Newsbeitrag
    news:bkso2q$qjt$uk.sun.com...
     

    On a properly configured system, there should be absolutely no need for
    /etc/md.conf. However, the file could be used as a reference.
     

    This is going about it in a slightly false way. What needs to be done is to
    run the `metaroot` command, which modifies the /etc/vfstab so that the /
    device is /dev/md/d0.

    That way, if one of the /dev/md/d0 disks should fail, the kernel md driver
    boots from the other good disk, which should also contain the meta database
    s and should be made bootable with the `installboot` command. This
    way, the OS is totally oblivious of the fact that the other drive is
    buh-bye.

    Ideally, submirrors d1 and d2 should be devices on separate controllers.


    Solaris Guest

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