ch —
SCSI media changer driver
ch* at scsibus? target ? lun ?
The ch driver is essentially an
  ioctl(2) interface to a robot on
  a SCSI bus - a device that will change media (e.g. tapes, CD-ROMs, etc) in and
  out of drives for that media. The
  chio(1) utility program uses this
  interface to manipulate such robots.
  - /dev/chu
- SCSI bus media changer unit u
/usr/include/sys/chio.h
  - ch%d: waiting %d seconds for changer to settle...
- Some changers require a long time to settle out, to do tape inventory, for
      instance.
- ch%d: offline
- The changer is not responding.
- ch%d: warning, READ ELEMENT STATUS avail != count
- ch%d: could not sense element address page
- ch%d: could not sense capabilities page