Tape xfers topping out at 10K per transaction?

[Kevin A. Pieckiel]

On Wed, Oct 06, 2004 at 10:24:16PM -0500, Dan Nelson wrote:
> In the last episode (Oct 06), Kevin A. Pieckiel said:
> > I've got an Exabyte M2 connected to my system.  I'm running version
> > 5.2.1 and have seen this drive do 64K transfers with "systat -vm"
> > before (although that was under version 4.9).  I can't for the life
> > of me find out why I'm only getting 10K per transaction while I'm
> > reading from my tape now.  At the rate it's going, it will take over
> > 10 hours to read through the entire thing.  I know the tape drive is
> > capable of reading an entire tape in about three hours.
> 
> Tar defaults to a 10k blocksize.  When creating tapes, use the 'b'
> flag to specify blocksize in 512-byte units.  For a 64k blocksize:
> "tar cvbf 128 /dev/sa0 /usr"

I hit the same 10K limit when I use something like this:

# dd if=/dev/nsa0 of=/dev/null bs=64k

Is that because tar wrote to the tape with a 10k bock size that even
dd can't read larger blocks?  That doesn't seem likely to me, but
then again, what do I know?