On Wed, June 17, 2009 14:52, Tom Birkenbach wrote:
> The short question:
> How do you enable hardware compression on a tape drive (LTOx) in the Sun
> Solaris 8 and 10 operating system?

Use the /dev entry with the "c" in it.

> As I understand Solaris, the difference between the ./0cbn and the ./0ubn
> is that "c" represents enabling of "standard compression" where "u"
> represents enabling of "ultra compression".  I'd like to try and enable
> ultra compression, but when I remove the tape drive and do a rescan of
> the tape library, it always comes back with the "c" and never gives me
> a chance to put in the "u".
>
> Any thoughts on how to reconfigure an existing drive OR bring in the drive
> as desired?

While Solaris does list different file entries for different ways you want
to use a tape drive, not all "modes" are applicable to all drives. From
the st(7D) man page:

    /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 den-
         sity, BSD behavior, and no rewind.
   [...]
        For 8mm tape devices (Exabyte 8200/8500/8505):

         l                             Standard 2 Gbyte format
         m                             5 Gbyte format (8500, 8505 only)
         h,c                           5 Gbyte compressed format (8505 only)

         For 4mm DAT tape devices (Archive Python):

         l                             Standard format
         m,h,c                         data compression

You can see that for some technologies only certain things are possible.
It may be that for LTO-3 there is no "ultra" compression mode--or rather
it's probably that "ultra density" mode is simply the normal compression
system that LTO-3 provides; the 'u' and 'c' may be synonyms in a sense,
and Sun simply decided to only make the 'c' option visible.

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