In my experience, you gain a 14% increase in capacity by using the 
non-compression device on highly compressed (i.e. gzip) data.   However, I 
just chose to take the capacity hit rather than do something like Justin 
proposes.   Therefore my DLT8000 tapes were maxing out at 34G-35G instead 
of the native 40G.   Other drive types might be different though.

-Jon

On Wed, 21 Jan 2004, Rockey Reed wrote:

> Justin,
> 
> Don't mess with turning the compression off on the tape drive.   If the data
> is already compressed the tape drive will not affect it.  You gain nothing
> and make management a nightmare if you try to work with compression on/off
> depending on the backup policy.  However, if you insist on doing a bn/cbn
> configuration, I recommend having two or more drives and configure one
> without compression, put it in a separate storage unit and use that STU for
> the backup of the file system.
> 
> HTH,
> Rockey 
> 
> -----Original Message-----
> From: veritas-bu-admin AT mailman.eng.auburn DOT edu
> [mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu] 
> Sent: Wednesday, January 21, 2004 1:29 PM
> To: veritas-bu AT mailman.eng.auburn DOT edu
> Subject: [Veritas-bu] Changing tape drive paths
> 
> I am just now setting up a backup system using NBU 4.5MP6 on a Sun
> Enterprise 5500 server running Solaris 9.
> 
> Most of the data I will be backing up is typical Unix and Windows stuff,
> plus some Oracle databases.  However, on my SAN I have a 6 TB filesystem
> that will eventually be about 95% full.  The vast majority of that data will
> already be compressed (using a proprietary format), so I would not want to
> use the hardware compression device.  But for everything else (presumably) I
> would want to use compression.
> 
> The only way I can think to handle this is to use, for example,
> 
>     tpconfig -update -drive 0 -path /dev/rmt/0bn
> 
> in a notify script (maybe session_start_notify) and then
> 
>     tpconfig -update -drive 0 -path /dev/rmt/0cbn
> 
> in the corresponding end script (session_notify).  If I were to do this, I
> know I would need to make sure that the 6 TB filesystem is the only one that
> would run in the session.
> 
> Does anyone have experience with this sort of a situation, or am I just
> overlooking a better method of handling this?
> 
> Thanks,
> 
> Justin
> 
> 
> --
> Justin C. Lloyd
> Unix System Administrator
> MCI System Technology Solutions
> Office 703.886.3219 Vnet 806.3219 Fax 703.886.0132
> 
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