[Dump-users] Corruption of recently-modified file contents

[Ben H. <bj...@ca...>]

I've recently found that some of the dumps produced by dump don't 
correctly record certain files.  In the example that brought this 
problem to my attention, a file that was created six hours before dump was 
run was recorded in the dump as consisting entirely of zeroes, which it 
didn't when viewed through the filesystem.

I can easily reproduce the problem using the following test script:

i=0
while sleep 1; do
  echo $$.$i > testfile.$$.$i
  /sbin/dump -0f - . 2>/dev/null | /sbin/restore -Cf -
  i=$(($i + 1))
done

After a few iterations, there will usually be some test files that 
repeatedly appear different in tape and disk copies, and they can 
continue to be dumped incorrectly for tens of minutes at least (I've not 
yet run the test for longer).

Running "sync" doesn't seem to help matters.  Running "blockdev 
--flushbufs" does help, in that files created before the flush start 
appearing correctly, but it can only be run by root, which makes it a 
bit of a nuisance to set up.

Is this behaviour to be expected?  Does it represent a bug in either dump 
or Linux?  How do other people deal with it?

My tests have so far been on the following systems:

SUSE LINUX 10.1 (X86-64)
  dump 0.4b41-14
  kernel 2.6.16.27-0.6-smp
  e2fsprogs 1.38-25.9
  glibc 2.4-31.1

SUSE LINUX Enterprise Server 9 (i586)
  dump 0.4b35-41.1
  kernel 2.6.5-7.283-smp
  e2fsprogs 1.38-4.18
  glibc 2.3.3-98.73

Debian testing/unstable
  dump 0.4b41-2
  kernel 2.6.15-1-amd64-k8-smp
  e2fsprogs 1.38+1.39-WIP-2005.12.31-1
  libc6 2.3.6-10

Sample dump output is:

  DUMP: Date of this level 0 dump: Wed Feb  7 14:56:10 2007
  DUMP: Dumping /dev/sda5 (/home (dir /dump/test)) to standard output
  DUMP: Label: none
  DUMP: Writing 10 Kilobyte records
  DUMP: mapping (Pass I) [regular files]
  DUMP: mapping (Pass II) [directories]
  DUMP: estimated 804 blocks.
  DUMP: Volume 1 started with block 1 at: Wed Feb  7 14:56:10 2007
  DUMP: dumping (Pass III) [directories]
  DUMP: dumping (Pass IV) [regular files]
  DUMP: Volume 1 completed at: Wed Feb  7 14:56:10 2007
  DUMP: Volume 1 800 blocks (0.78MB)
  DUMP: 800 blocks (0.78MB)
  DUMP: finished in less than a second
  DUMP: Date of this level 0 dump: Wed Feb  7 14:56:10 2007
  DUMP: Date this dump completed:  Wed Feb  7 14:56:10 2007
  DUMP: Average transfer rate: 0 kB/s
  DUMP: DUMP IS DONE

-- 
Ben Harris, University of Cambridge Computing Service.  Tel: (01223) 334728