dd curiosity

Joseph Sarkes joe at junkyard.UUCP
Tue Jan 2 05:55:34 AEST 1990

In article <396 at zok.UUCP>, mark at zok.UUCP (Mark W. Snitily) writes:
> partition.  Noticed a large speed difference based upon the direction
> of the I/O.
> For example, if I write 4 sectors into the partition starting at sector
> 20000, the write will complete very fast, (i.e. a few seconds):
>       dd if=myfile of=/dev/rdsk/0p1 seek=20000 count=4
> But, if I read 4 sectors from the partition starting at sector 20000,
> the read will take forever to complete, (i.e. we're talking minutes to
> hours depending upon the skip value):
>       dd if=/dev/rdsk/0p1 of=myfile skip=20000 count=4

dd skip= READS over the amount specified. See if your dd command has an
option iseek= instead of using skip=.
This should seek over the space instead of reading all of it.
You can either use strings /bin/dd | grep iseek,
or just try using the option and look for an error message.

I understand that some raw devices also have problems seeking, so
you may have better luck using iseek with a block device.

Joseph Sarkes	(junkyard!joe)

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