Very Computer

   (Alan Rollow - Dr. File System's Home for Wayward Inodes.) writes

Quote:>If there is a difference in the block size and the blocking factor,
>this is probably it.  One is the I/O size used by the application
>(ufsdump) and the other is the internal block size that the drive
>uses.

On some HP MPE machines I used to work on, "Blocking Factor" was
a number specifying the number of records to write to each block
on the tape.  Block size was simply the BF multiplied by the record
length.  For example, a BF of 20 with a record length of 500 gave a
block size of 10000.

Some further clarification on the efficiencies affected by BF
(again, at least in the context of the HP 3000's I used)

As a tape is written from the machine, a block's worth of data is
read from the disk file, then written to the tape.  Consequently,
smaller block sizes (which result from lower BF's) result in more
reads to transfer a file, and consequently much more time spent
on disk to tape I/O.

Also, each block on the tape is separated by physical space, so
more blocks on the tape (again, from a low BF) result in
more "unused" space - tape not occupied by data.  I've had tapes
run out of room from use of a too-low BF (and take
much too long to write), that were able to hold the file(s) when
the BF was increased (more data per block = less tape
used for physical space between blocks -> the file fit on the tape)

Mike

My opinions are mine and not necessarily those of my employer, who
has no opinions except when it comes to those of its employees...