Help using dd
in [UK Linux]
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From: Chris Davies on 7 Dec 2009 16:50 Richard Kettlewell <rjk(a)greenend.org.uk> wrote: > Experimentally the default for coreutils dd is to be 512 bytes at a > time, although if this is documented I don't immediately see where. The Debian man page, along with at least Solaris, includes this or words to this effect: bs=BYTES read and write BYTES bytes at a time (also see ibs=,obs=) ibs=BYTES read BYTES bytes at a time (default: 512) obs=BYTES write BYTES bytes at a time (default: 512) HTH Chris
From: Richard Kettlewell on 7 Dec 2009 17:39 Chris Davies <chris-usenet(a)roaima.co.uk> writes: > Richard Kettlewell <rjk(a)greenend.org.uk> wrote: >> Experimentally the default for coreutils dd is to be 512 bytes at a >> time, although if this is documented I don't immediately see where. > > The Debian man page, along with at least Solaris, includes this or > words to this effect: > > bs=BYTES > read and write BYTES bytes at a time (also see ibs=,obs=) > > ibs=BYTES > read BYTES bytes at a time (default: 512) > > obs=BYTES > write BYTES bytes at a time (default: 512) > > HTH Ah, I was looking at the version in lenny, which doesn't document the defaults. -- http://www.greenend.org.uk/rjk/
From: Chris Davies on 8 Dec 2009 12:33 Chris Davies <chris-usenet(a)roaima.co.uk> writes: > The Debian man page [...] includes this or words to this effect: Richard Kettlewell <rjk(a)greenend.org.uk> wrote: > Ah, I was looking at the version in lenny, which doesn't document the > defaults. I've got "testing" coreutils, 7.4-2, which has this in the changelog: 2009-02-19 Jim Meyering <...@redhat.com> doc: dd: document that the default block size is 512 bytes * src/dd.c (usage): Document the default block size. * doc/coreutils.texi (dd invocation): Document that the default block size (bs, ibs, obs) is 512 bytes. Reported by Petr Uzel. HTH Chris
From: alexd on 8 Dec 2009 14:02 Meanwhile, at the uk.comp.os.linux Job Justification Hearings, jasee chose the tried and tested strategy of: > Are you suggesting using ntfs-3g (supposed to be very good I know with > full read write access to ntfs volumes) recover option (no thanks!) or > norecover? The latter similar to force in mount.ntfs. Sorry, saying 'here' was possibly a little misleading; I meant for when trying to mount an NTFS volume under Linux that wasn't cleanly unmounted, not necessarily for when trying to recover data from a dicky disk. -- <http://ale.cx/> (AIM:troffasky) (UnSoEsNpEaTm(a)ale.cx) 18:49:27 up 10 days, 22:40, 7 users, load average: 0.00, 0.00, 0.00 Plant food is a made up drug
From: Theo Markettos on 9 Dec 2009 20:23
jasee <jasee(a)btinternet.com> wrote: > Theo Markettos wrote: > >> Really? dd uses sector access, which should be about as quick as > >> you can get. Or do you mean it slows down a lot when it needs to > >> retry? > > > This is what I've heard (100 times) and from my experience this time > it certainly is, even without the errors I'm getting this time. If you use the small default blocksize it can make a difference. For example, to CompactFlash in my USB1.1 reader: $ sudo dd bs=512 if=openwrt-x86-ext2.image of=/dev/sdb 107439+0 records in 107439+0 records out 55008768 bytes (55 MB) copied, 211.396 seconds, 260 kB/s $ sudo dd bs=1048576 if=openwrt-x86-ext2.image of=/dev/sdb 52+1 records in 52+1 records out 55008768 bytes (55 MB) copied, 104.753 seconds, 525 kB/s Theo |