Re: dd for failing discs?

[Bernhard Voelker]

On 02/12/2014 12:47 PM, Bernhard Voelker wrote:
> Thanks, I'll prepare a patch for the docs, then.

Here is a proposal.

Have a nice day,
Berny


>From 7f73ea7a32f731baef49b4e8988f0b3c7618a983 Mon Sep 17 00:00:00 2001
From: Bernhard Voelker <address@hidden>
Date: Thu, 13 Feb 2014 00:32:48 +0100
Subject: [PATCH] doc: add dd example for failing disks

* doc/coreutils.texi (dd invocation): Add an example for how to call
dd to save data from a failing disk.  Mention GNU 'ddrescue' as one
of the more specialized tools in such a case.
---
 doc/coreutils.texi | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 3269291..e2339f3 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -8927,6 +8927,22 @@ tape=/dev/rmt/0
 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
 @end example

+@cindex ddrescue
+@cindex disks, failing
+For failing disks, other tools come with a great variety of extra
+functionality to ease the saving of as much data as possible, e.g.
+@uref{http://www.gnu.org/software/ddrescue/, GNU @command{ddrescue}}.
+However, in cases where such a tool is not available or when the administrator
+feels more comfortable with the handling of @command{dd}, calling it with the
+options @samp{iflag=fullblock} to avoid short reads and 
@samp{conv=sync,noerror}
+to pad out unreadable parts and to continue on read errors might be
+helpful as well:
+
+@example
+# Rescue data from an (unmounted!) partition of a failing disk.
+dd conv=noerror,sync iflag=fullblock </dev/sda1 > /mnt/rescue.img
+@end example
+
 Sending an @samp{INFO} signal to a running @command{dd}
 process makes it print I/O statistics to standard error
 and then resume copying.  In the example below,
-- 
1.8.4.5