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

[DePriest, Jason R.]

On 7/24/07, stephbal1wrote:
> 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?

It will not corrupt the array.  You are saving the image to a .img
file which is good.

> -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?

Yes.  When it runs out of space, maybe even a bit before depending on
your OS, it will stop.  Not a good idea as it could cause some
stability problems.

Can you create a compressed volume or something like that and put the
image file there temporarily?

If you are on a network, can you put a netcat listener on a system
with more space?

> -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?.

That wouldn't guarantee that you get the data you want.

> -Q4- [How] Do I know the 18GB I want will be in these first 20GB, and not 
> scattered all over the drive?

You can't unless you do some sort of analysis of the disk and find out
where the data you want is physically located.

> 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

Good luck!

-Jason

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