Thanks to all who responded to my questions. The answers are
pretty uniform, Exabyte 8500 can not do compression. The rst24,25
drivers merely send a density code to the tape drive, and 8500 can not
understand this code. It does not have the required hardware. Several
people suggested using software compression, unfortunately, it is not
applicable here.
Thanks to:
dave@goose.ca.pdc.com (dave)
Mike Raffety <mike_raffety@il.us.swissbank.com>
Dave Fetrow <fetrow@biostat.washington.edu>
cfoley@arsenic.cray.com (Chuck Foley)
syd@dsinc.myxa.com (Syd Weinstein)
david.warm@fi.gs.com (David Warm)
glenn@uniq.com.au (Glenn Satchell - Uniq Professional Services)
epl@Kodak.COM (Gene Loriot (epl@Caps.Kodak.COM.))
cecilp@vancouver.cantel.rogers.com (Cecil Pang)
worsham@aer.com (Robert D. Worsham)
louis@meg.meg.saic.com (Dances on keyboards (Louis Brune))
pluta@eda.mke.ab.com (Rick Pluta)
==============dave@goose.ca.pdc.com (dave) ==========
Compression in controlled by the firmware in the drive. If you have an
8500 and not an 8500c or a 8505, you cannot do compression. Conversley, if
you had an 8500c or an 8505 and you did NOT want to write in compression,
you could control that by specifying a different device name. I believe that
/dev/rst8 for an 8500c or 8505 would be the device name to use if you did not
want to write in compression.
==============Mike Raffety <mike_raffety@il.us.swissbank.com> ===========
Just do the compression on the CPU ... like this:
dump 0bsdf 126 6000 54000 - | compress | dd of=/dev/rst8 bs=126b
===============Dave Fetrow <fetrow@biostat.washington.edu> ============
You can play games like this:
ln -s /dev/nrst0 .norewind
mt -f /dev/nrst0 rewind
tar cf /user/disk0 | compress > .norewind
tar cf /user/disk1 | compress > .norewind
===============cfoley@arsenic.cray.com (Chuck Foley)===============
While the 8500C and 8505 support compression, the 8500 does not.
===============syd@dsinc.myxa.com (Syd Weinstein) ===============
In the 8500C and 8505, compression is performed in hardware in the drive.
The 8500 just doesn't have the hardware. The different minor numbers
just tell the driver what set mode command to tell the drive.
==================glenn@uniq.com.au (Glenn Satchell - Uniq Professional Services) ===========
No, the 8500c and 8505c both have extra hardware in them that does the
compression, although I believe you can get an 8500 upgraded to do the
compression.
For a 8500 (or I guess an 8200) you can do things like:
tar cvf - | compress | dd of=/dev/rst8 obs=63k
dump 0uf - /file/system | compress | dd of=/dev/rst8 obs=63k
but this will take a lot of extra cpu resources to compress on the fly.
===============epl@Kodak.COM (Gene Loriot (epl@Caps.Kodak.COM.))======
I have tried the compression device (/dev/rmt/0c on Solaris 2.3) with no luck,
apparently the 850nC is different that the 850n drive.
==============cecilp@vancouver.cantel.rogers.com (Cecil Pang)=========
The 8500C and 8505 both has hardware compression where 8500 has none.
The answer is NO.
=============worsham@aer.com (Robert D. Worsham)============
No, the 8500 does not have the compression hardware of the 8500c and
8505.
============louis@meg.meg.saic.com (Dances on keyboards (Louis Brune))======
The 8500 doesn't do compression. It *can* do 8200 mode, for about 2.3
vendor-gigabytes/tape, and it can do 8500 mode for about 5
vendor-gigabytes/tape, but neither of these involve data compression.
===========pluta@eda.mke.ab.com (Rick Pluta)============
You can't use a 8500 in compression mode as the required hardware is not there.
When you specify the rst24,25 devices, the driver tries to send the density
code (0x8c) which denotes compression to the drive. I believe this causes an
error which you are seeing as "no tape loaded".
=============End of Summary================
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