Old DDS/4mm Tape drive speed issues

Ok, so I bought a tape drive from ebay..its a Dell PowerVault 100T dds4 tape drive (internal seagate std1400lw).  I really like the 4mm tape format because theyre so small.  Just perfect for freezing my usual data output (some notes, documents).

At first I thought I bought a lemon, since the drive was super slow.  As usual I played around with block sizes.  Normally I leave the blocksize to 512, which is usually what I find tape drives to have the default set up as.  I usually would do this:

mt -f /dev/st1 setblk 512  # if necessary
tar cvfp /dev/st1 ....

Or, sometimes, If I want the default tar blocking factor to be the same as the hardware block size:

mt -f /dev/st1 setblk 10240 # thats 20 tar blocks of 512 each
tar cvfp /dev/st1 ...

But the tape drive is SUPER SLOW no matter how I tried...Until I tried 4096 (page size?) on a whim.  And this drive just flew!  So this is how to make this drive spin fast:

mt -f /dev/st1 setblk 4096 # page size
tar cvfpb /dev/st1 8 ...
tar tvfb /dev/st1 8 .....

What a surprise that was.. and I was using tapes for years.

--------------UPDATE-------------

20190918

The slow speed is for READING BACK DATA, not writing them.  For some reason the tape drive stalls delivering data for data transfers > 4k.  Therefore, to read back data, specify transfer buffers of 4k or less:

mbuffer_style#  mbuffer -s 4096 -i /dev/st2 | tar tvf -
normal_tar# tar xvfpb /dev/st2 8



JondZ 20190917