prc@erbe.se (Robert Claeson) (05/19/89)
I generally use blockfactor 20 when I'm reading and writing
1600 bpi tapes, but I haven't found a good blockfactor for
6250 bpi tapes yet. The speed seems to be much lower at the
higher (6250) density with a blockfactor of 20, and it doesn't
improve much with higher factors (I've tried up to 128).
If anyone uses a blockfactor that gives good performance at
6250 bpi, I'd really like to know what it is. Please reply
via e-mail.
--
Robert Claeson E-mail: rclaeson@erbe.se
ERBE DATA ABchris@mimsy.UUCP (Chris Torek) (05/20/89)
In article <687@maxim.erbe.se> prc@erbe.se (Robert Claeson) writes: >I generally use blockfactor 20 when I'm reading and writing >1600 bpi tapes, but I haven't found a good blockfactor for >6250 bpi tapes yet. Nine track tapes have poor error recoverabilty beyond 10240-byte records at 1600 bpi. Error correction on GCR drives is better, so that although the bits are packed more densely, records of up to 32768 bytes are generally safe (`GRAS' is the sci.med-ish term :-) ). Tar's `blocking factor' values are in terms of 512 bytes: `b 20' is 10240 bytes, and `b 64' is 32768 bytes. Cartridge tapes (generally *not* 6250 fci) are often implemented such that the actual records on the tapes are always 512 bytes long, no matter what size is used to write to them. Here only write (or readback) speed matters when choosing a block size. Otherwise, larger blocks are generally better as they waste less tape on inter-record gaps. -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris