zftape only. Set block length to count bytes.
The default block size of zftape is 10kb which matches the default of the
GNU tar
program. The argument count has to be a multiple of
1024 (including 0). Due to the QIC-113 standard
(http://www.qic.org) a maximum block size of 62kb is allowed. An
argument of `0
' means to switch to variable block size mode. This
is implemented in zftape by setting the internal block size variable
zft_blk_sz
to `1
' and thus has some unexpected side affects
on the MTFSR
, MTBSR
and MTSEEK
ioctls which
interpret their arguments in units of zft_blk_sz
bytes,
i.e. they take their argument as a byte count when zftape is in variable
block size mode.
When writing a volume, the block size used for the volume is stored in the corresponding volume table entry, (see MTIOCVOLINFO), because the driver needs to remember the block size of a tape volume when using compression.
When reading a volume one has to use the block size the volume was
created with. There is no need use the MTSETBLK
ioctl again but
the read count has to be a multiple of the original block size.
mt -f /dev/nqft0 setblk 63488
mt -f /dev/nqft0 setblk 0
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