On Sat, Mar 29, 2008 at 11:30:25PM +0200, Dag Nygren wrote:
> At least all the DLT drives have a "capacity mode" and a "performance mode"
> with the  following features:
> 
> Capacity mode:
> - Would always stop the reels when no more data available
> - thus always uses the tape to it's full extent
> 
> Performance mode:
> - Will "fill" with empty data up to a certain amount if no data
> in the buffer. Just in case there would be some available later...
> - This avoids start/stop of the tape as much as possible
> - Will waste a lot of space when the data stream is below the
> native speed. My worst case is 40% wasted.

Do you know of any documentation with that description for the modes?
The DLT 7000 product manual describes them in this manner:

PERFMODE              When set, the drive is tuned for
                      performance.

                      When cleared, the drive is tuned for
                      capacity.

                      The default for 4 MB cache tape drives is 1
                      (performance mode). In performance mode,
                      compression is turned off to keep the drive
                      streaming, thus improving performance. If PERFMODE
                      is 0 on 4 MB cache tape drives, then compression
                      is turned on, resulting in better capacity.
                      PERFMODE is ignored by 8 MB cache tape drives.

There's no mention of writing voids.

> The modes were selectable with a jumper in early DLT drives, but
> later this jumper was hard soldered, because of bad 
> performance/publicity, using the  capacity mode.

The 4MB version of the DLT 7000 performed poorly at lower speeds.  All
later versions of the drive were 8MB and performance mode is not
selectable.

-- 
Darren Dunham                                           ddunham AT taos DOT com
Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
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