>Yup.  The FSM driver basically wedges itself between the
>kernel/processes and the lower level disk drivers.  When the
>filesystem is full, rather than returning a full condition to the
>kernel/process, it blocks the process and tries to clear off
>space.  Once enough space is available, the process can then
>continue.  Likewise, when the kernel/process tries to read a migrated
>file, the driver blocks the process while it restores the data from
>the ADSM server.

I wish it would consistently actually do this; but more often than not, I see
attempts to write into an HSM file system get "File system full" conditions,
and retrievals get "Device not ready", making for rather inconvenient restarts
of the intended operations.  HSM "sort of works", but is so flakey that I'm
sure we're not the only site not wanting to give it to ordinary users.
    Richard Sims, BU