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.<br><br>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.<br>
<br>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.<br><br>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.<br>
<br>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.<br>
<br><div class="gmail_quote">On Tue, Oct 27, 2009 at 3:36 PM, John Lange <span dir="ltr"><<a href="mailto:john@johnlange.ca">john@johnlange.ca</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Just out of curiosity, what is it that these various programs that<br>
people have recommended do with regard to imaging that "dd" doesn't?<br>
<br>
I've never looked at any of these in any great detail but so far as I<br>
can see they all add complexity while reducing functionality.<br>
<br>
Image a disk? dd<br>
<br>
Backup a file system? rsync<br>
<br>
to tape? tar<br>
<br>
to remote? ssh (or scp)<br>
<br>
scheduled? put any of the above in cron<br>
<br>
That's all you need. What am I missing?<br>
<br>
Regards,<br>
<div class="im">--<br>
John Lange<br>
<a href="http://www.johnlange.ca" target="_blank">http://www.johnlange.ca</a><br>
<br>
</div><div class="im">On Tue, 2009-10-27 at 15:26 -0500, Montana Quiring wrote:<br>
> This is from Clonezilla page:<br>
> Based on Partimage, ntfsclone, partclone, and dd to clone partition.<br>
> However, clonezilla, containing some other programs, can save and<br>
> restore not only partitions, but also a whole disk.<br>
><br>
> Thanks for the feedback everyone!<br>
<br>
<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Dan Martin, MD<br>GP Hospital Practitioner<br>Computer Scientist<br><a href="mailto:ummar143@shaw.ca">ummar143@shaw.ca</a><br>(204) 831-1746<br>answering machine always on <br>