Node cloning

Josip Loncaric josip at icase.edu
Fri Apr 6 10:11:27 EDT 2001


"Robert G. Brown" wrote:
> 
> > On Thu, 5 Apr 2001, Oscar Roberto [iso-8859-1] López Bonilla wrote:
> >
> > > And then use the command (this will take long, so you can do it overnight)
> > >          cp /dev/hda /dev/hdb ; cp /dev/hda /dev/hdc ; cp /dev/hda /dev/hdd
> 
> [...]  This approach to cloning
> makes me shudder -- things like the devices in /dev generally have to
> built, not copied, there are issues with the boot blocks and bad block
> lists and the bad blocks themselves on both target and host.  raw
> devices are dangerous things to use as if they were flatfiles.

I agree.  Whatever the protections built into today's drives, there are
still plenty of bad blocks that Linux needs to map out, and the
information about them is stored in the filesystem.  This disk dependent
information must be built, not copied.

BTW, we found that about 10% of our IDE hard drives (mostly early
Seagate 7200rpm UDMA models) had either too many bad blocks or bad
blocks in unacceptable locations (like the swap partition) and had to be
replaced.  We now use a combination of Seagate and IBM drives, and over
the past two years about 20% of them have developed at least some bad
blocks that we had to map out using the 'e2fsck -c ...' command.  

I read somewhere that the overall PC industry average fraction of disk
drive problems is 17%.  This is quite significant, and if you are more
careful about your disks than an average PC user, chances are that
you'll find that 20-30% of the drives have some kind of problem. 
Unfortunately, some cloning approaches (e.g. systemimager) do not
include the 'badblocks' program to check the new disk *before*
installation (although the check can be done after installation, this
could be too late). 

Maintaining 1TB's worth of local disks on a cluster of machines requires
regular monitoring.  We check for problems monthly and fix them as
needed.  

Sincerely,
Josip
 
-- 
Dr. Josip Loncaric, Research Fellow               mailto:josip at icase.edu
ICASE, Mail Stop 132C           PGP key at http://www.icase.edu./~josip/
NASA Langley Research Center             mailto:j.loncaric at larc.nasa.gov
Hampton, VA 23681-2199, USA    Tel. +1 757 864-2192  Fax +1 757 864-6134

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