dd questions

dragonember · 08-23-2008, 07:09 PM

I need to copy a windows drive that is probably starting to fail. It is an old drive, probably 7-8 years old and certain files are randomly getting deleted and the computer is getting slower and slower. A system restore did not help. This to me suggests that the hard drive is beginning to fail. Unfortunately the computer is old and I don't believe the motherboard is equipped with S.M.A.RT. capabilities.

My questions:
1. can dd copy a windows partition from a live linux cd (i assume the answer to this is yes since it make a byte exact copy)

2. if I copy the 20GB hard drive to an image file then write that image using dd again to a 40GB hard drive, will the other 20GB be lost due to the new hard drive thinking it is a 20GB drive? The reason I ask this is because I was reading that since dd performs low level raw data manipulation that any new hard drive will be made to think it is the old one. Therefore, one would have to use the same type, model, and size hard drive. However, I do not know if the information I read was correct or not.

Thanks.

lensman3 · 08-26-2008, 09:42 PM

Yes, dd does do device level reads and writes. I heard, a long time ago, that if a sector was bad on the read it was written as bad on the write. This had to do with copying CD's and DVD's. So bad sectors were written. This probably happens when you dd copy a hard drive. (I think dd will copy an unmounted disk, so the copied disk can be quiet when you copy it).

If you copy a 20 GB disk to a 40 GB disk, you will loose the 20 GB. I think you could partition the disk into 2 - 20GB parts and copy the bad disk to the second partition by: "dd if=/dev/sda1 of=/dev/sdb2".

Before you do the dd or cp, run fdisk on the drive so that all the inodes and files have a semblance of being OK.

Why don't you just mount the drive and use "tar" or "cp -pr" to copy the disk. At least then the disk drivers will try to read the "correct" bytes off the disk. I think you could even use "cp /dev/hda1 /dev/hdb1". Copy, cp, will copy the hard devices too. The only problem is that if your old disk was bootable, chances are it won't be bootable after the copy. I think lilo or grub need to know the exact sector to boot from. You will probably have to re-assign the boot address.

I hope this helps.

08-23-2008, 07:09 PM	#1 (permalink)
dragonember Registered User Join Date: Jan 2006 Location: The voices in my head disagree... Posts: 163 OS: Windows XP: Home Edition SP2/Ububtu 8.04 My System	dd questions I need to copy a windows drive that is probably starting to fail. It is an old drive, probably 7-8 years old and certain files are randomly getting deleted and the computer is getting slower and slower. A system restore did not help. This to me suggests that the hard drive is beginning to fail. Unfortunately the computer is old and I don't believe the motherboard is equipped with S.M.A.RT. capabilities. My questions: 1. can dd copy a windows partition from a live linux cd (i assume the answer to this is yes since it make a byte exact copy) 2. if I copy the 20GB hard drive to an image file then write that image using dd again to a 40GB hard drive, will the other 20GB be lost due to the new hard drive thinking it is a 20GB drive? The reason I ask this is because I was reading that since dd performs low level raw data manipulation that any new hard drive will be made to think it is the old one. Therefore, one would have to use the same type, model, and size hard drive. However, I do not know if the information I read was correct or not. Thanks. __________________ Extrico subjectio quod verum ero evidens No one can make you feel inferior without your consent. -- Eleanor Roosevelt "it may be alright to be content with what you have; never with what you are."--B.C. Forbes

08-26-2008, 09:42 PM	#2 (permalink)
lensman3 Registered User Join Date: Oct 2007 Location: Littleton, Colorado USA Posts: 470 OS: xp 64 sp2 Fedora Core 8 (vmware xp core 8 x32) Minix	Re: dd questions Yes, dd does do device level reads and writes. I heard, a long time ago, that if a sector was bad on the read it was written as bad on the write. This had to do with copying CD's and DVD's. So bad sectors were written. This probably happens when you dd copy a hard drive. (I think dd will copy an unmounted disk, so the copied disk can be quiet when you copy it). If you copy a 20 GB disk to a 40 GB disk, you will loose the 20 GB. I think you could partition the disk into 2 - 20GB parts and copy the bad disk to the second partition by: "dd if=/dev/sda1 of=/dev/sdb2". Before you do the dd or cp, run fdisk on the drive so that all the inodes and files have a semblance of being OK. Why don't you just mount the drive and use "tar" or "cp -pr" to copy the disk. At least then the disk drivers will try to read the "correct" bytes off the disk. I think you could even use "cp /dev/hda1 /dev/hdb1". Copy, cp, will copy the hard devices too. The only problem is that if your old disk was bootable, chances are it won't be bootable after the copy. I think lilo or grub need to know the exact sector to boot from. You will probably have to re-assign the boot address. I hope this helps.