At least on Solaris 2.6, "u" and "c" are the same : they are linked 
to the same (major,minor) pair, as shown below :

# ls -lL /dev/rmt/1[uc]bn
crw-rw-rw-   1 root     sys       33,1117 Apr  2  1998 /dev/rmt/1cbn
crw-rw-rw-   1 root     sys       33,1117 Apr  2  1998 /dev/rmt/1ubn

I suppose "c" is Unix standard, while "u" is a Solaris specific naming 
convention.

Don't forget that depending on the compression ratio, you will put
quite different amount of datas. The only guaranted capacity is 20 Gb.
Now suppose you store some 1:10 compressible text data files, you'll
put about 200 Gb of original data on a single DLT tape.

---
Sebastien DAUBIGNE 
sebastien.daubigne AT sema DOT fr <mailto:sebastien.daubigne AT sema DOT fr>  - 
(+33)
(0)5.57.26.56.36
Sema Global Services - AFM/DW/Pessac

        -----Message d'origine-----
        De:     Stephen.Liss AT attbi DOT com [SMTP:Stephen.Liss AT attbi DOT 
com]
        Date:   lundi 10 décembre 2001 18:33
        À:      veritas-bu AT mailman.eng.auburn DOT edu
        Objet:  [Veritas-bu] Tape capacity

        have you tried other options other than 'u'?
        how about 'c'?


        from st(7D):


        <snip>

        /dev/rmt/[0- 127][l,m,h,u,c][b][n]

        where l,m,h,u,c specifies the density (low, medium, high,
ultra/compressed),
        b the optional BSD behavior (see mtio(7I)),
        and n the optional no rewind behavior.
        For example, /dev/rmt/0lbn specifies unit 0,
        low density, BSD behavior, and no rewind.



        <snip>





        I think if you don't say 'c' you  may not be using compression






        |-----Original Message-----
        |From: veritas-bu-admin AT mailman.eng.auburn DOT edu
        |[mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu]On Behalf Of 
Noel
        |Lindsay Hunt
        |Sent: Sunday, December 09, 2001 2:23 AM
        |To: Veritas BU
        |Subject: [Veritas-bu] Tape capacity
        |
        |
        |I am having big problems writing to a Quantum DLT4000.
        |This drive is attached to an Ultra 2 which was running a
        |set of dump scripts using ufsdump, writing to the `ultra'
        |compressed device, `/dev/rmt/0ubn', dumping roughly 41Gb,
        |well within the capacity of the compression device.
        |
        |This machine has now become a media server, and the
        |storage unit is this drive, using the same device file,
        |but NetBackup is exiting after writing something less
        |than 40Gb. The bptm log file even shows it reads EOM from
        |the tape (unless I am sorely mistaken). I can't
        |understand what is happening. As far as I can see this
        |shouldn't happen. Has anyone any experience with this
        |problem?
        |_______________________________________________
        |Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu
        |http://mailman.eng.auburn.edu/mailman/listinfo/veritas-bu
        |
        |

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