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    SubjectRe: limits on raid
    On Tue, 19 Jun 2007, Lennart Sorensen wrote:

    > On Mon, Jun 18, 2007 at 02:56:10PM -0700, wrote:
    >> yes, I'm useing promise drive shelves, I have them configured to export
    >> the 15 drives as 15 LUNs on a single ID.
    >> I'm going to be useing this as a huge circular buffer that will just be
    >> overwritten eventually 99% of the time, but once in a while I will need to
    >> go back into the buffer and extract and process the data.
    > I would guess that if you ran 15 drives per channel on 3 different
    > channels, you would resync in 1/3 the time. Well unless you end up
    > saturating the PCI bus instead.
    > hardware raid of course has an advantage there in that it doesn't have
    > to go across the bus to do the work (although if you put 45 drives on
    > one scsi channel on hardware raid, it will still be limited).

    I fully realize that the channel will be the bottleneck, I just didn't
    understand what /proc/mdstat was telling me. I thought that it was telling
    me that the resync was processing 5M/sec, not that it was writing 5M/sec
    on each of the two parity locations.

    David Lang
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