Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!snorkelwacker!spdcc!mirror!premise!junkyard!joe
From: joe@junkyard.UUCP (Joseph Sarkes)
Newsgroups: comp.unix.i386
Subject: Re: dd curiosity
Summary: skip vs. iseek
Message-ID: <592@junkyard.UUCP>
Date: 1 Jan 90 18:55:34 GMT
References: <396@zok.UUCP>
Lines: 23

In article <396@zok.UUCP>, mark@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)