(rescue hard disk helper)
bash script to manage dd_rescue conveniently
|FAQ||(Frequently asked questions)|
READMEWhat is dd_rhelp ?
dd_rhelp is a bash script that handles a very usefull program written in C by
Kurt Garloff which is called dd_rescue, it roughly act as the dd linux command
with the caracteristic to NOT stop when it falls on read/write errors.
This makes dd_rescue the best tool for recovering hard drive having bad
sectors. (dd_rescue can be found: http://www.garloff.de/kurt/linux/ddrescue )
But using it is quite time consuming. This is where dd_rhelp come to help.
In short, dd_rhelp will use dd_rescue on your entire disc, BUT it will try to
gather the maximum valid data before trying for ages on bunches of
badsectors. So if you leave dd_rhelp work for infinite time, it'll have the
same effect as a simple dd_rescue. But because you might not have this infinite
time (this could indeed take really long in some cases... ), dd_rhelp will jump
over bad sectors whenever it encounters too much in a row. In the long run,
it'll parse all your device with dd_rescue.
You can Ctrl-C it whenever you want, and rerun-it at will, it'll resume it's
job as it depends on the log files dd_rescue creates.
In addition, progress will be shown in a ASCII picture of your device beeing
As stated by Kurt Garloff for his dd_rescue program: "Just one note: It does
work. I unfortunately did not just create this program for fun ..."
dd_rhelp goes the same as it has saved me YEARS on my hard drive.
Important note :
For some times, dd_rhelp was the only tool (AFAIK) that did this type of job,
but since a few years, it is not true anymore: Antonio Diaz did write a ideal
replacement for my tool: GNU 'ddrescue'.
Yes, this is not very clever to have called a tool the same name that
'dd_rescue' from Kurt Garloff (catch the subtle difference between 'ddrescue'
and 'dd_rescue' ?), but it seems that it was done by intent as we warned
Antonio Diaz from the fact it would probably mess users in this tiny world of
hard drive recovery tools.
Nevertheless, I really encourage you to use this replacement tool if it works
for you (and it should be the case). Why ? Understand first what we are
- dd_rhelp (in dirty bash script) + dd_rescue (in C) in one hand
- ddrescue (in C) in the other.
dd_rhelp was meant as a quick hack to implement what dd_rescue didn't do, and
what couldn't be done at that time (AFAIK).
It could be some cases where ddrescue won't work, and this is the major reason
why I keep maintaining dd_rhelp. It is important to tell me and Antonio Diaz
when these cases occur.
Now that you are enlightened, you are free to use dd_rhelp.
Why do people want to use dd_rhelp ?
Well, you do not WANT to use dd_rhelp. I hope you'll never HAVE TO use it.
Basically, if you have bad sector corrupting your filesystem you'll have
several solutions depending on the filesystem itslef, the partition table, and
what remains accessible...
In some recovering process, as a first stage, you'll need to secure all the
remaining data of your disk (or partition) in a file or partition on a
healthier device. Often, next operation is to fsck.* your recovered data to
rebuild the damaged filesystem information. Whith chance, you will be able to
mount the result and access files. These could then be in various states
depending of how they have been affected by the damages. Possible file states
are ranging from completely recovered without any further work, to lost,
damaged, scrambled, and often anonymously collected in your filesystem
dd_rhelp and dd_rescue are meant to be in the very first phase only: securing
your remaining data into a another file.
dd_rescue which has been created by Kurt Garloff, is a great program. And could
already help you without dd_rhelp. But in some case, like disks cluttered with
bad sectors, it can be time consuming to use for 2 main reasons :
1 - it does straight recovery, and thus can spend months making it's path in a
solid bunch of bad sectors before rescuing hole portions of perfectly sain data
hidden just after.
2 - if you decide to manoeuver dd_rescue to stop him when he's bumping in large
sequences of bad sectors and try to start it from spots to spots in normal or
reverse direction (as dd_rescue options allows this), then this can require a
lot of YOUR time.
It is where dd_rhelp comes to help: it is a wrapper for dd_rescue. This means
it'll call it with various arguments to change it's start position or the
direction of the scanning process. It'll guide dd_rescue into a new behavior
which will lead to rescuing much more data in the beginning of the process all
over the disk.
If you didn't really understood, here's another explanation :
Why do people want to use dd_rhelp ? (v2)
This can really take a long time if you have much bad sectors. (and I had this
As bad sectors tends to be in large groups and these groups seems to tend to
be dispatched on drive, and if you just launch dd_rescue on the beginning of
your drive and there is a large group of bad sectors coming next, you could
be waiting for years before rescuing any data. While waiting, your anxiety will
be free to grow as you won't have answer to these dreadful questions:
- Is there any valid data to rescue AFTER this chunk ?
- How big is this chunk ?
- When will I get answer to these two first question ?
So your solution with dd_rescue is to stop dd_rescue, and "jump" ahead randomly
and try to copy from a chosen offset. Then you could again fall on a group of
and then you should stop dd_rescue and jump somewhere else on your drive.
This behavior involves the user's constant presence (you !).
The idea of the dd_rhelp shell script is to do this job: launching dd_rescue
for you on the disk while trying to get the max amount of data out of your disk
in a minimum of time. It'll be jumping over bad blocks, using the reverse copy
option of dd_rescue to pin out bad sector group and rescue as much data as you
could have rescued manualy.
Why use dd_rhelp and not dd_rescue ?
This is a good question. dd_rhelp uses dd_rescue to compute a recovery path
through the device that will focus on valid data recovering. This recovery path
will go through all the device, exactly as dd_rescue could do it on its own
without any path. This means that dd_rhelp will save you time ONLY IF YOU
INTEND TO CANCEL ITS JOB BEFORE THE END of a full recovery.
Why wouldn't you want a full recovery ? because a considerable amount of time
is taken to try to rescue badsectors. This amount of time can be mesured in
days, month, years, depending on your device capacity and its
defectiveness. You might not want to spend this time knowing that 99 percent of
this time will be taken to look at badsector and won't lead to any more data
dd_rhelp shifts this useless waiting time to the end of the process. Using
dd_rescue straight throughout your device make waiting time dependent on the
Think about dd_rescue standalone if you only intend (and can afford) to wait
until a full dd_rescue scan. dd_rhelp optimizes only the order in which this
full scan will occur to focus on recovery of what will be recoverable in
first. So in the end, launching dd_rhelp for a full scan will take exactly the
same time dd_rescue would have taken plus a considerable time which correspond
to the overhead of calculating its path.
How should I use it ?
Since version 0.1.0, you WON'T NEED to do this step:
> First build it from sources, with "./configure && make"
> Optionnaly run "make install"...
This shell script is very basic and not well written, but it supports the
"--help" and "--version" of GNU Coding Standard. It should be quite
straight-forward to use.
so go for a :
When running dd_rhelp you can safely Ctrl-C, or kill dd_rhelp, it'll resume its
job the next time you call it.
Olivier SANTIANO, a french dd_rhelp user shared his experience of complete
process of recovering his hard drive with dd_rhelp and post-dd_rhelp recovery
work: http://f1efq.free.fr/save.htm (in french)
How do I install this package ?
Since 0.1.0, dd_rhelp is directly usable (you can copy it to a directory in
your path, or use it directly out of the box).
How does it work ?
dd_rhelp uses log files made by dd_rescue. Precisely, it searches for the
"Summary report" that dd_rescue prints when its job is over.
1 - dd_rhelp creates itself an internal representation of what has been parsed
2 - It'll find the greatest part of the disk that hasn't been tested and will
launch dd_rescue from the middle of this part backwards, then forwards until
it rescues without error all data, or until it falls on 5 consecutive read
3 - go back to step 1 unless everything has been dd_rescued...
It worked fine for me (home made distrib) on big harddrives (partitions of 15
Gigs). Received positive feedbacks on large partition (60 Gigs and 200 Gigs),
and it should only be limited by the linux kernel limitation. Though the bash
script could be longer to compute next position in very large disk with lots of
bad sectors scatered all over your disk.
It worked on Debian, Ubuntu, and on a Knoppix CD. After each release, I test it
on a knoppix with a 1.44M diskette with badsectors or a damaged CD-ROM/DVD-ROM.
Darwin/MacOSX should be supported. This support is erratical, so more feedback
If you have any other experiences of dd_rhelp, please let me know.
IMPORTANT NOTE :
This shell script needs version >= 1.03 of dd_rescue !!!!
I want to look in the code, but it's really complicated
Yes, I know. This is a big bash script because I rely on a personnal shell
library which finishes included nearly completely at the beginning of the
Feel free to modify, give hint or else.
We are all knowing that a quick C program should be better. So feel free to
create it ! And this is what Antonio Diaz did for its "GNU ddrescue" program,
make sure to have a look to it before using dd_rhelp.