On Jun 28, 2007, at 1:31 PM, Avy Wong wrote:

Richard,
      Let me see if I understand this right.  You mentioned, " The
compression algorithms in tape drive hardware are usually the
best.......", ,so  the tape drive has a built in setting that
automatically
compresses the data. Or do they have to be set manually? When can
locate
this setting?

As I said, you define that compression should be used, via the TSM
Devclass.  This results in the TSM server software issuing the
appropriate system call through the device driver, typically via ioctl
(), as in a STIOCSETP operation, when then issues that order to the
tape drive to latch the setting.  The drive then compresses all data
being written to the drive.  And, of course, decompression occurs on
reading, to the point of it returning to the form originally sent by
the client.  When the client gets the data back, it may do its own
decompression, if it had also compressed the data.  You can see gory
detail in the Atape device driver programming reference manual.

   Richard Sims