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Re: [Libguestfs] [libvirt-users] Suggestions on building VM disks from scratch



On Wed, Apr 04, 2012 at 09:45:18AM +0100, Richard W.M. Jones wrote:
>   # 9GB sda1
>   part-add /dev/sda p 64 $(( 9*1024*1024*2 ))
>   # remainder in sda2
>   part-add /dev/sda p $(( 9*1024*1024*2 + 1 )) -64

This leaves the swap partition unaligned :-(

If you care about alignment (and you probably should) then this will
create properly aligned partitions:

  part-add /dev/sda p 128 $(( 9*1024*1024*2 - 1 ))
  part-add /dev/sda p $(( 9*1024*1024*2 )) -128

'Course the 'virt-alignment-scan' tool can be used to detect if your
partitions are aligned correctly.  With the original image:

  $ virt-alignment-scan -a test.img 
  /dev/sda1        32768           32K   bad (alignment < 64K)
  /dev/sda2   9663676928          512    bad (alignment < 4K)

With the correctly aligned image:

  $ virt-alignment-scan -a test.img 
  /dev/sda1        65536           64K   ok
  /dev/sda2   9663676416      1048576K   ok

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org


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