[Bug 945001] [NEW] Erase data very slow compared to standard dd wipe

[Robert Ayres]

Public bug reported:

'Erase data' option is very slow on a newly created dm-crypt device.  On
my 4k sector disk, it took approx. 4 hours to complete 10% of a ~700Gb
device wipe.  I cancelled the process, then opened a shell and used a
simple 'dd if=/dev/zero of=/dev/mapper/sda5_crypt bs=1M' and wiped the
device in around 2-3 hours (much more expected)!

It looks like blockdev-wipe is responsible for the device wipe.  Not
sure if it's the block size the installer uses being too small - 65536
or the fact the device is opened with the 'O_SYNC' flag.

'Erase data' is disabled by default but for those of us who do wish to
use it, it'd be nice if you didn't have to exit the installer to a
temporary shell to issue a 'dd' wipe.

Ubuntu Release: Ubuntu 11.10 amd64 Alternate CD

** Affects: partman-crypto (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/945001

Title:
  Erase data very slow compared to standard dd wipe

Status in “partman-crypto” package in Ubuntu:
  New

Bug description:
  'Erase data' option is very slow on a newly created dm-crypt device.
  On my 4k sector disk, it took approx. 4 hours to complete 10% of a
  ~700Gb device wipe.  I cancelled the process, then opened a shell and
  used a simple 'dd if=/dev/zero of=/dev/mapper/sda5_crypt bs=1M' and
  wiped the device in around 2-3 hours (much more expected)!

  It looks like blockdev-wipe is responsible for the device wipe.  Not
  sure if it's the block size the installer uses being too small - 65536
  or the fact the device is opened with the 'O_SYNC' flag.

  'Erase data' is disabled by default but for those of us who do wish to
  use it, it'd be nice if you didn't have to exit the installer to a
  temporary shell to issue a 'dd' wipe.

  Ubuntu Release: Ubuntu 11.10 amd64 Alternate CD

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