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    SubjectRe: IBMs LVM ?
    On Sep 11, 2001  17:26 +0200, Christoph Hellwig wrote:
    > > I heard rumors about IBM porting their LVM code from AIX to Linux.
    >
    > IBM has an OpenSource volume manager called evms, and although
    > it does support AIX Volumes is has it's root in IBM's OS/2
    > volume management system. (I believe someone at IBM thinks of PCs
    > when hearing Linux so all their ports start from OS/2...)

    Actually, this isn't quite correct. Yes, the EVMS folks started with
    the LVM design from OS/2 (which was based on AIX LVM, but not compatible).
    However, IBM DID GPL the AIX 4.3 LVM code, and there IS support for AIX
    VGs under EVMS.

    > > Will it be replaced with the one from IBM ?
    >
    > ALthough the current LVM has its's issues I hope not so - the current
    > EVMS is the best example on hhow to not write kernel subsystems.

    Do you have a specific complaint? The current LVM kernel code isn't all
    that robust either (and the user-space code is not very pretty).

    I DO think that EVMS will replace the current LVM code in the kernel. Why?
    - It already has 100% compatibility with the current LVM on-disk layout.
    - It already has 100% compatibility with AIX LVM code.
    - It is already possible to do LVM autoconfig of volumes within the kernel
    without needing an initrd to activate the volumes.
    - It removes knowlege of partitions out of the disk drivers and makes them
    a simple form of LV.
    - It is already possible to use partial Linux-LVM volumes (i.e. use LVs
    that are 100% available in a VG, even if a disk is bad/missing). You
    can't do that with the current LVM (sometimes you can't even do it if
    ALL of the disks are there).
    - The AIX LVM on-disk metadata layout is FAR more robust than the current
    LVM metadata layout. While this is supposed to be fixed for Linux-LVM
    at some point, the previous Linux-LVM changes have been TERRIBLE with
    respect to compatibility, while EVMS is DESIGNED to support multiple
    on-disk metadata layouts.
    - It is possible (not done yet) to add things like NT Logical Disk Manager
    (NT LVM-stuff) into EVMS.
    - It is possible (not done yet) to add HPUX LVM/veritas/OSF volume stuff.
    - It is possible to merge MD RAID support into EVMS also, to support all
    of the different RAID layouts with common code*.

    All in all, instead of having things like striping/RAID-1/concatenation/
    RAID-5 reimplemented in each subsystem (e.g. LDM/MD/veritas/etc) we can
    take the current MD code and make it a layer in EVMS which can handle all
    of these cases.

    (*) While the exact on-disk layout of each RAID implementation may vary
    slightly (block sizes, stripe widths, etc), I'm guessing that the majority
    of it is common enough that we can re-use the existing MD code (parity
    calculation, resync, etc) to handle most kinds of RAID-0/1/5 setups.

    Cheers, Andreas
    --
    Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto,
    \ would they cancel out, leaving him still hungry?"
    http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert

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