On several different machines, all with "options NTP" and ntp4, with
several different SCSI host adapters, both in 1.5 and in current with
thorpej-scsipi, I've noticed that if I push the 'st' driver hard, two
things happen:

1) Output periodically pauses; the result is that the tape doesn't stream
   for more than perhaps 30 seconds at a time.  Whether I have four striped
   SCSI disks feeding a DLT8000 on a separate SCSI bus or a single IDE disk
   feeding a DLT2000XT, I can sustain well above the drive's continuous
   write rate for some time, but inevitably there's a pause that causes
   the tape to stop streaming.

2) ntpd periodically must adjust the clock by about 0.5-1.5 *seconds* while
   the tape drive is in use.

I think something is losing clock interrupts.  Ideas?  Has anyone else
seen this?  I've seen it with adw, ahc, and isp HBAs and DLT2000, DDS3,
and DLT8000 tape drives; the tape drives are always on their own bus.

-- 
Thor Lancelot Simon	                                      tls@rek.tjls.com
    And now he couldn't remember when this passion had flown, leaving him so
  foolish and bewildered and astray: can any man?
						   William Styron