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    SubjectRe: Quick question on Software RAID support.
    On Wed, 13 Feb 2002, Alan Cox wrote:

    > > Is it supposed to detect a failed disk and *stop* using it?
    > Yes, it will stop using it and if appropriate try and do a rebuild

    So I guess something went wrong in my case.
    The disk died bad. You could hear (from outsite the rack the PC was
    mounted on) a repeated sound of "Ziing -> TOC!". There's no way now to make
    a BIOS (or a DOS test tool) detect it.

    > > I had a raid1 IDE system, and it was continuosly raising hard errors on
    > > hdc (the disk was dead, non just some bad blocks): the net result was that
    > > it was unusable - too slow, too busy on IDE errors (a lot of them - even
    > > syslog wasn't happy).
    > Don't try and do "hot pluggable" IDE raid it really doesn't work out. With
    > scsi the impact of a sulking drive is minimal unless you get unlucky

    Does the above apply to ATA HW RAID controllers, too? I mean, is it
    something strictly related to electrical specs of the interface or
    is it possible to find workarounds? (whether a vendor apply them with
    success it's another story - I wonder if it's possible in theory)

    Anyway, the problem is not replacing the disk, is to have the system
    stop using it - automatically, without human action. If you say it is so,
    then I just must have been unlucky.

    > (I have here a failed SCSI SCA drive that hangs the entire bus merely by
    > being present - I use it to terrify HA people 8))

    the topic here is data safety, what do HA people know about it? B-)

    Again, do HW RAID ATA controllers have an hope to handle a failure better
    than the average IDE controllers you find integrated into a typical MB?

    Right now, to implement a 2+ disks RAID (sw) with IDE/ATA, I'd put
    one disk per channel, on some multi-channel controllers (i.e. some
    HPTs you've mentioned below). I'm just curious if RAID HW support brings
    something new into the game... Here I'm considering resilience, not
    performance: I know (by experience) that 2 disks in the same channel
    is a small gain performance-wise. I'm tempted to buy an HPT RocketRAID
    133 (just to name one): it supports (on paper / web) "disk mirroring,
    hot-spare options for automatic array-rebuilds, hot-swap support for
    swapping failed disks on the fly [...], and disk failure notification".
    I still think SW RAID is better, since I don't really like relying
    on a black box (read: some unknown firmware).

    > > BTW, given a 2 disks IDE raid1 setup (hda / hdc), does it pay to put a
    > > third disk in (say hdb) and configure it as "spare disk"? I've got
    > > concerns about the slave not actually beeing able to operate if the
    > > master (hda) fails badly.
    > Well placed concerns. I don't know what Andre thinks but IMHO spend the
    > extra $20 to put an extra highpoint controller in the machine for the third
    > IDE bus.
    > Alan


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