Re: CDROM jukebox filesystem using autofs

Steve McIntyre (
Sun, 3 May 1998 17:07:59 +0100 (BST)

H. Peter Anvin writes:
>> Are you suggesting that when disks 1-4 are mounted and busy
>> and I do an ls on /autofs/5, the ls gets an EBUSY? This doesn't
>> make much sense. Normal small CDROM jukeboxes I have seen working
>> under Linux allow you to have all of the disks mounted and they swap
>> disks as necessary. These are done by multiplexing at the block
>> device level so you get a /dev/scd0 - /dev/scd5 for a 6 disk
>> changer. The jukebox I am writing a driver for has hundreds of
>> disks so it seems impractical to do this -- hence my autofs
>> approach. Using the autofs model, the only choices I have are to
>> grant a request from the kernel or say it doesn't exist (the process
>> gets a File not Found and a negative dentry is created). I can
>> modify autofs to also support sending an EBUSY but is this desired?
>I think the way to do this is going to involve some amount of disk
>caching if you want it to work sanely.

Yes, very much so. In fact at this point it's probably worth looking at
some of the commercial implementations of this kind of thing. For example,
I know that Plasmon ship copies of Manager, a jukebox control/interface
product, with most of their jukeboxes. This makes the jukebox itself
appear as a single filesystem, with subdirectories below that for each
disk in the system. Add persistent caching of file and meta data...

Steve, not speaking for Plasmon even if he does work for them...

Steve McIntyre, CURS CCE, Cambridge, UK.
<a href=>My home page</a>
"Can't keep my eyes from the circling sky,                 +------------------
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