Help with a little dd damage!

Ian Malone ibmalone at gmail.com
Wed Feb 27 23:50:07 UTC 2008


Brian Chadwick wrote:
> Ian Malone wrote:
>> Brian Chadwick wrote:
>>> Morgan Read wrote:
>>

>>>> [root at morgansmachine DiskBUImagesEtc]# dd if=/dev/sda 
>>>> of=2ndstage.rescue bs=1K count=1280
>>>> 1280+0 records in
>>>> 1280+0 records out
>>>> 1310720 bytes (1.3 MB) copied, 0.0535238 s, 24.5 MB/s
>>>> [root at morgansmachine DiskBUImagesEtc]# chown morgan: ./2ndstage.rescue
>>>> [root at morgansmachine DiskBUImagesEtc]# dd if=zImage-LAB-20060421.htc 
>>>> of=/dev/sda
>>>> 2348+0 records in
>>>> 2348+0 records out
>>>> 1202176 bytes (1.2 MB) copied, 0.117155 s, 10.3 MB/s
>>>> [root at morgansmachine DiskBUImagesEtc]#
>>>>
>>

>>
>> The point was Morgan has an accidental sort-of backup of the bit
>> he dd-ed over.
>>
> he copied 1280 blocks .... then overwrote it with 2348 blocks ... the 
> damage is done
> 

Different block size: 1310720 bytes copied first (1K BS), 1202176 copied
second (512B BS).  If more had been copied the earlier (33M) dd might
have been of some use, depending on what exactly is at the start of the
disk, but if / is /dev/sda1 then probably give up.

Interesting aside, both block-sizes are on the small side
(understandable given the intent of copying a pda boot image),
this may be why the first copy gets about twice the rate -
limited by the rate of copy operations.

-- 
imalone




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