I have used dd for copying drives or partitions in the past, in order to have a clone ready to swap in in the event of a failure. I found it extremely useful, much faster than some cheap commercial software.
One problem I have encountered is IO errors, especially when copying large volumes. The 'noerr' option allows the copy to complete, but of course does not correct the problem. I have had one or two errors on every second drive.
For my Mac, I have some commercial software that can find the error and what file (if any) it affects. It can report the error to the HSF+ file system, so that no other files use that sector.
I can't find any material that explains how this works -- what I surmise is that the drive firmware hides defective blocks. Obviously it does not hide them all, or at least not instantly - so the file system tracks bad blocks that the firmware has missed in order to avoid using them in files. Using dd circumvents the file system, so there is a risk of a corrupt file on the target drive/partition.
The drives seem OK in every other respect, and software that monitors the status of the drives does not indicate any impending failure. I am guessing, based on a small sample, that this is a 'normal' condition.
On Tue, Oct 27, 2009 at 3:36 PM, John Lange john@johnlange.ca wrote:
Just out of curiosity, what is it that these various programs that people have recommended do with regard to imaging that "dd" doesn't?
I've never looked at any of these in any great detail but so far as I can see they all add complexity while reducing functionality.
Image a disk? dd
Backup a file system? rsync
to tape? tar
to remote? ssh (or scp)
scheduled? put any of the above in cron
That's all you need. What am I missing?
Regards,
John Lange http://www.johnlange.ca
On Tue, 2009-10-27 at 15:26 -0500, Montana Quiring wrote:
This is from Clonezilla page: Based on Partimage, ntfsclone, partclone, and dd to clone partition. However, clonezilla, containing some other programs, can save and restore not only partitions, but also a whole disk.
Thanks for the feedback everyone!
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