Mailinglist Archive: opensuse-factory (279 mails)

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Re: [opensuse-factory] cloning a hard drive with YaST
  • From: Greg Freemyer <greg.freemyer@xxxxxxxxx>
  • Date: Tue, 10 Mar 2009 06:45:57 -0400
  • Message-id: <87f94c370903100345s3c9b6713i939e4371d709f505@xxxxxxxxxxxxxx>
On Tue, Mar 10, 2009 at 12:05 AM, Carlos E. R.
<robin.listas@xxxxxxxxxxxxxx> wrote:
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On Monday, 2009-03-09 at 23:26 -0400, Greg Freemyer wrote:

dd if=/dev/sda of=/dev/sdc bs=1G conv=noerror

Please note, never use noerror without also using sync.

Why? I'm curious. I can make a guess, but I'm not sure, it is not mentioned
in the manual:

      noerror
             continue after read errors

      sync   pad every input block with NULs to ibs-size; when used
             with block or unblock, pad with spaces rather than NULs

Do you mean, that without "sync", the output would just skip the remaining
bytes of a block after an error, meaning the output would simply be
"smaller", with pieces missing?

Because, as Sid did an 'xfs_repair' on the result, it means either there was
no error, or that the gaps were filled :-?

Look at the output of a dd run.

dd if=/dev/zero of=/dev/null count=100
100+0 records in
100+0 records out
51200 bytes (51 kB) copied, 0.000172439 s, 297 MB/s

The first 100 says 100 blocks read without error. the first zero is 0
failed blocks failed to read.

The second 100 is the blocks written without error, and the second 0
is the failed block writes.

If you don't use sync and there are 2 errors I believe you get:

98+2 records in
98+0 records out.

i.e The failed blocks are not replicated in the destination at all

With sync, you get:
98+2 records in
100+0 records out.

I'm not sure what the exact output block has in it but at least part
of it is zero filled. I always use a 4k block size to align my
userspace behavior with the kernels normal page size.

Greg

- -- Cheers,
      Carlos E. R.

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Greg Freemyer
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