Help using dd
in [UK Linux]
|
Prev: Firefox/DNS problem, possibly due to two ADSL lines, advice needed
Next: spamassassin with thunderbird
From: jasee on 5 Dec 2009 02:00 Simon J. Rowe wrote: > jasee wrote: > >> Whats the advantage? Some versions dd_rescue and ddrescue (seperately >> maintained, I know) will copy in reverse if there is a bad block, but >> simple dd will continue using 'noerror' AFAICT. > > But dd will merely skip the bad block so you'll have a hole in your > FS. dd_rescue will (at worst) substitute a block of zeros > You should be able to use sync with dd to give the same effect though gives nulls apparently >so you have a chance of rescuing data. Maybe, but if you're recovering an ntfs partition then having a block of zeros here or there will probably confuse the life out of NT's NTFS (chkdsk) :-) THe main problem with any of these facilities is the slowness; which is exactly what you don't want with disk recovery. dd disk access is apparently 100 times slower than normal disk access and from what I've done I can imagine that is correct. And if the structure is damaged it seems to take much longer! Anything which takes more time or is more intensive has big disadvantages.
From: jasee on 5 Dec 2009 02:37 Following up my own post (bad, I know) but as no-one has corrected my post, to send dd's output to a file, you need to mount a partition or have one already mounted with write access. Depends on the live cd, I think. Mounting it makes it viewable. (I think that if you are logged on as root you will automatically have write access?)
From: Chris F.A. Johnson on 5 Dec 2009 03:33 On 2009-12-05, jasee wrote: > > Following up my own post (bad, I know) but as no-one has corrected my post, > to send dd's output to a file, you need to mount a partition or have one > already mounted with write access. To send the output to a file, you just have to give it the path to a file. Yes, that filepath does have to be on a mounted partition, or it is not a valid filepath. .... > (I think that if you are logged on as root you will automatically have write > access?) If the filesystem is mounted, yes. -- Chris F.A. Johnson <http://cfajohnson.com> Author: ======================= Pro Bash Programming: Scripting the GNU/Linux Shell (2009, Apress) Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)
From: jasee on 5 Dec 2009 08:11 Paul Martin wrote: > In article <0Jmdncied8CfmIfWnZ2dnUVZ8qydnZ2d(a)bt.com>, > jasee wrote: > >> THe main problem with any of these facilities is the slowness; which >> is exactly what you don't want with disk recovery. dd disk access is >> apparently 100 times slower than normal disk access and from what >> I've done I can > > Set a block size. The default is to read a character at a time. That's > inefficient. I'm setting it to 4096, can I set it higher?
From: Anahata on 5 Dec 2009 09:48
On Sat, 05 Dec 2009 13:11:04 +0000, jasee wrote: > Paul Martin wrote: >> Set a block size. The default is to read a character at a time. That's >> inefficient. > > I'm setting it to 4096, can I set it higher? Yes. I think I used 1M once, but I didn't verify whether it actually helped with speed. -- Anahata anahata(a)treewind.co.uk -+- http://www.treewind.co.uk Home: 01638 720444 Mob: 07976 263827 |