Dumping to an exabyte tape drive

[Dave Martindale]

In article <439 at cfa.HARVARD.EDU> wyatt at cfa.HARVARD.EDU (Bill Wyatt,OIR) writes:
>
>In any case,
>choosing a blocking that's a multiple of 8k will mitigate this loss, so
>I can't understand why a blocking factor of 126 (63k) is often recommended.
>A blocking factor of 56k=112 should be better.

Yes, a blocking factor of 8k should minimize part-track writes.  But this
only matters if, in fact, the host can't keep the tape supplied with
data.  The 8200 drive only writes 246 kb/sec, and the Berkeley-style
multi-buffered "dump" can easily supply that when reading data from
a decently fast disk when the system is otherwise not busy (typical
of overnight dumps).

If you're not worried about keeping up to the tape, then setting the
blocksize to 126 gives you the largest writes that are still a multiple
of 1k, which minimizes system overhead and time spent transferring
stuff on the SCSI bus.

The 8500 drive will change all this, since the transfer rate is
twice as fast.  But then, the track size is likely to be something
other than 8K too.