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    SubjectRe: Mirroring Root Disks

    You have made an eligant point; regardless, I do not do what you propose
    because ATA ...... the kernel does not yet know how to fake the OS in
    switch to get a boot in a failure.

    I will trump the debate with a $2600.00 ATA-Hardware RAID solution I
    showed at LWE@NYC.NY 2000.

    $2600.00 == 320GB (8x40GB ATA Disks) and an 8-channel Host (3ware).
    This was a RAID 0 stripe.

    Imagine that you can remove the disks and shuffle in any order (on the
    same card) and it finds-reconstructs the RAID?

    SCSI can not touch 320GB in disks for $2600.00 USD.

    On Fri, 11 Feb 2000, Martin Bene wrote:

    > At 00:48 11.02.00 -0800, Andre Hedrick wrote:
    >
    > >> Is there a good way to mirror Root disks.
    > >>
    > >> Is RAID-1 only options for mirroring under Linux or something else is
    > avialable.
    > >> If RAID-1 is the only option, how safe, fault tolerant it is.
    > >>
    > >> I fear setting up RAID for root, as any problem with RAID may make
    > system unbootable. Any
    > >> comments. suggestions links on Root disks mirroing ????
    >
    > >Do hardware RAID..........ATA or SCSI but that is you only bet.
    >
    > Granted - Hardware Raid is probably the most stable and professional
    > solutin - it's not the only one however:
    >
    > You CAN have software raid for every part of your disk, including /.
    >
    > A few pointers on software raid:
    >
    > * have a look at the howto on http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
    > * You want to use the raid 0.90 code available as patches for 2.0 and 2.2
    > kernels, not the code included in the kernel tree
    > * With the 0.90 raid code, / on raid (any type - 0 / 1 / 4 / 5 work equaly
    > well) is no problem, the raid arrays get initialized by the kernel on
    > bootup and can be mounted just like any other device.
    > * Swap on raid is currently problematical - I think background
    > resynchronisation of mirror drives conflicts with use as swap; if you
    > ensure that no resynchronisation takes place while the device is used as
    > swap, it should work. Swap on raid would only make sense for mirror or
    > raid5 to gain reliability.
    >
    > The only bit of configuration that's still a bit tricky is where to keep
    > the stuff needed by the bootloader to get a kernel into memory; usually the
    > stuff stored in /boot for lilo configurations. There are several ways of
    > dealing with /boot stuff:
    >
    > * have a seperate non-mirrored /boot1, /boot2 etc. on each of the disks
    > containing mirrors of your / filesystem, have lilo write startup info to
    > each disk by having a seperate lilo.conf for each disk.
    >
    > * have /boot on a raid1 mirror and use a patched version of lilo (patch by
    > redhat available in the redhat 6.1 source stuff). The patched lilo can
    > handle raid1 mirror devices and will make each of the devices in a mirror
    > bootable.
    >
    > As for stability: The linux raid 1/4/5 code can handle failing disks
    > without requiring user interaction; you have to be careful with your setup
    > however - some errors have to be avoided to allow continued operation in
    > case of a drive failure:
    >
    > * Don't put two parts of a raid device on the same IDE bus (master/slave)-
    > chances are that a failing master drive will take a slave on the same cable
    > with it, causing two drives to fail at the same time -not good. Besides, it
    > wont help performance either.
    >
    > * If you're using SCSI, be careful which controllers / drivers you use -
    > some drivers don't handle failing disks well at all and will lock up your
    > system or slow it to a crawl by stubbornly trying to access the dead disk
    > and resetting the bus on failure indefinitely if a disk goes down.
    >
    > Bye, Martin
    >
    >
    > "you have moved your mouse, please reboot to make this change take effect"
    > --------------------------------------------------
    > Martin Bene vox: +43-316-813824
    > simon media fax: +43-316-813824-6
    > Andreas-Hofer-Platz 9 e-mail: mb@sime.com
    > 8010 Graz, Austria
    > --------------------------------------------------
    > finger mb@mail.sime.com for PGP public key
    >

    Andre Hedrick
    The Linux ATA/IDE guy


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