On Thu, 15 Mar 2001, Byron Stanoszek wrote:
> I have a real picky tape drive (DLT series) that likes to be fed large chunks
> of data at once, otherwise after every 2-4KB of data it halts and rewinds
> itself because its cache for writing to the tape is empty.
>
> My best solution to this problem was to use 'tar -b 4096', which sends 4096 x
> 512-byte blocks at once for a total of a 2MB buffer size. This worked fine for
> several weeks, until 2 days ago I got this message (and the backup fails):
>
> st: failed to enlarge buffer to 2097152 bytes.
>
The default maximum number of scatter/gather segments in the tape driver
is 16. This means that big chunks of memory are needed to allocate a 2 MB
buffer. You can increase the number of segments up to, e.g., 128. This
means that only 16 kB chunks are needed to make up a 2 MB buffer. The
number of scatter/gather segments is also limited by your SCSI adapter
driver. Note that even with 16 kB segments you may find problems at
some time because multi-page allocations are needed.
You can increase the number of scatter/gather segments at system
startup/module loading or when compiling the driver. See the file
linux/drivers/scsi/README.st for the syntax and st_options.h for the
compile-time definition.
Kai
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