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Quick Linux / RAID Questions

Posted on 2004-10-29
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Last Modified: 2013-12-16
Two quick questions...

1) We have a RAID5 array with 3 18GB SCSI disks.  The disk is not sold anymore, unfortunately.  As long as it matches the type of SCSI controller (U160, etc), are there any other potential issues which could prevent the RAID controller or Linux from being able to add a new and/or larger disk from a different manufacturer to the RAID array?

2) I have read that basically the two things you need to expand a RAID array partition is first, to fdisk the drive, delete the partition, and recreate with the same starting cylinder, but extending it to the full length.  And second, to use resize2fs to actually expand the partition.  Is this correct, and all that is needed?

Obviously a full set of backups would be ready before any steps were taken.

Thanks in advance.
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Question by:Wraezor
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    by:
    1.  You can use any SCSI disk as long as it's the same size or larger to replace a failed disk or to go from a 3 disk to a 4 disk or more container.  If you used a slower disk, all the drives would operate slower.

    2.  Sorry - can't help here.
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    by:grblades
    Hi Wraezor,
    2. I seriously doubt you can do this. The reason being is that RAID 5 splits the data across all disks evenly with one holding parity information. Therefore when you break the RAID 5 and recreate it with an additional disk the extra capacity does not just get added to the end of the logical drive so you cannot simply expand the partition.
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    by:Wraezor
    To clarify...grblades...

    It is hardware RAID.  Correct me if I'm wrong, but if it's done in hardware, doesn't that mean that the OS doesn't actually know anything about the RAID and accesses it as a regular disk?    In which case, I wouldn't be breaking my RAID, as my controller seems to support expansion of arrays.  I'm not worried about that though, I just don't know how the OS will handle it.
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    by:Wraezor
    Thanks leew...I'll give you 40pts for that, whenever pt 2 is answered.
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    by:grblades
    If it is hardware RAID and the controller supports extending the array then the OS will just see a larger disk. I haven't used reiserfs so cannot say what the procedure is to expand the partition. The procedure you mention though sounds as though it should work.
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    by:grblades
    Just looked up the procedure and you are correct.
    http://www.namesys.com/resize_reiserfs.html

    After resizing the partition you need to unmount it before you can perform the resize. Therefore if it is your boot partition you are resizing you will need to boot off a floppy or CD in order to perform the resize.
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    by:Wraezor
    Thanks grblades.

    Has anyone actually done a hardware RAID5 expansion using this method and can verify that it works in Linux?
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    Expert Comment

    by:grblades
    I don't personally know of anyone who has done it. If you have a spare machine lying around you could install Linux on it and not assign all the hard disk and then test the procedure for expanding the partition.
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