From: Chris Davies on
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
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
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
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
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