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    SubjectRe: CDROM jukebox filesystem using autofs
    On Thu, 30 Apr 1998, Dan A. Dickey wrote:
    > Aaron Passey wrote:

    > > So far, I have made it move and mount disks on command and unmount and put away
    > > disks in an LRU fashion. For example, if I do an ls of /autofs/1, it'll get
    > > the disk out of slot 1 and put it in one of the drives, mount it and give me
    > > the ls.
    > >
    > > There are several problems I am running into with this approach. First
    > > of all, what do I do if I have 4 drives, all mounted and busy, and I get a
    > > request for a fifth disk?
    >
    > return EBUSY.

    Or you could:
    - let the user of the first started request wait, and switch
    drives again after XXX kilobytes (making sure that throughput
    isn't hurt too much, latency will be bad anyway)
    - have a caching HD partition and read the biggest file requested
    for the next X MB, then quickly switch disks to the requested
    one

    > though it was an interesting exercise. Use Occam's (sp?) razor - simple is
    > better.

    For truly high-latency apps this might not be the case.
    Simply make sure that your readahead (on large files) is
    big enough (and maybe HD cached) so that no more than
    50% of the time/bandwidth is spent switching the disks.

    Rik.
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