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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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