[Bug-ddrescue] backingup a drive as a disk image onto a drive/array already in use

[stephbal1]

Hi,

Please accept my apologies for sending this email to the 'Bug-ddrescue' mailing 
list as I am asking for help and not reporting any bug. Disk failure is new to 
me and after days of searching through maunuals and forums I am still not sure 
my intended use of ddrescue is correct. Any help would be highly appreciated.

The PC my daily work relies upon has the following set up:
- unit 0, /dev/sda: a drive with the OS on, opensuse 10.0, with a size of 
290GB, and 18GB used.
- unit 1, /dev/sdb: a RAID 10 array, for the users accounts, with a size of 
~600GB, ~370GB used, and 220GB available.

The drive with unit 0 has 26 badblocks. I want to make a backup of that failing 
disk, eg as in the info file for ddrescue, section 6 'direct disc access', 
example 1. I do not have any new disk right now. I would therefore like the 
failing disk, the input, to be backuped as a disk image on the array, the 
output, without doing anything else (eg repartioning) to this array as I need 
it as it is.
Here is what I would try, from the rescue boot, having mounted the array on 
/dev/sdb1/:
ddrescue -n /dev/sda /dev/sdb1/users/lab/Documents/my_os_bu.img 
/dev/sda2/users/lab/Documents/my_os_bu.log
ddrescue -dr3 /dev/sda /dev/sdb1/users/lab/Documents/my_os_bu.img 
/dev/sda2/users/lab/Documents/my_os_bu.log
Here are my questions:
-Q1- Will the above usage of ddrescue corrupt the array and make the situation 
even worst?
-Q2- Will it try to copy the 290GB of unit 0 (/dev/sda) into the 220GB 
available on the array (/dev/sdb1/), and therefore fill up the array and fail 
to copy the OS drive entirely?
-Q3- To avoid this, should I rather use the -s option to tell ddrescue to stop 
after 20GB for example as I want the 18GB of data and not the entire, otherwise 
empty drive?.
-Q4- [How] Do I know the 18GB I want will be in these first 20GB, and not 
scattered all over the drive?

I pasted below output from 'mount', 'fdisk -l' and the /proc/partitions file.

I am stuck! Please help.

Best regards,

Stephane

%mount:
/dev/sda2 on / type reiserfs (rw,acl,user_xattr) 
proc on /proc type proc (rw) 
sysfs on /sys type sysfs (rw) 
tmpfs on /dev/shm type tmpfs (rw) 
devpts on /dev/pts type devpts (rw,mode=0620,gid=5) 
/dev/sdb1 on /local type reiserfs (rw,acl,user_xattr,usrquota,grpquota) 
usbfs on /proc/bus/usb type usbfs (rw) 
/dev/fd0 on /media/floppy type subfs 
(rw,nosuid,nodev,noatime,fs=floppyfss,procuid) 
/dev/hda on /media/dvdrecorder type subfs 
(ro,nosuid,nodev,fs=cdfss,procuid,iocharset=utf8) 


%fdisk -l /dev/sda2: 
Disk /dev/sda: 319.9 GB, 319988695040 bytes 
255 heads, 63 sectors/track, 38903 cylinders 
Units = cylinders of 16065 * 512 = 8225280 bytes 

  Device Boot      Start         End      Blocks   Id  System 
/dev/sda1               1        1045     8393931   82  Linux swap / Solaris 
/dev/sda2   *        1046       38903   304094385   83  Linux 


%more /proc/partitions: 
major minor  #blocks  name 

  8     0  312488960 sda 
  8     1    8393931 sda1 
  8     2  304094385 sda2 
  8    16  624977920 sdb 
  8    17  624968631 sdb1