(Alan Rollow - Dr. File System's Home for Wayward Inodes.) writes
>>After looking over the man pages for st and ufsdump in
>>Solaris, I am still confused as to what the differendces
>>are between a block size for a tape and
>>the blocking factor for the tape. Any tape gurus answer
>>this quick one for me?
My 2 cents worth: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
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)
My opinions are mine and not necessarily those of my employer, who
has no opinions except when it comes to those of its employees...