CentOS - Oct 2010 - Howto align partitions in Linux + NetApp

Hi,

NetApp support has suggested us aligning partitions to improve 
performance, in short: starting sector must be divisible by 8. How can I 
move the start point in a misaligned partition -in production, with 
ext3- under Linux?

A screenshot with a misaligned (start=63s) and aligned (start=64s) 
partition is available at:

	http://filesocial.com/lkwvvn2

(If anyone is interested in this topic, NetApp has a good document 
explaining performance issues in misaligned partitions: "Best Practices 
for File System Alignment in Virtual Environments", http://goo.gl/EkBw)

I have tried using parted "resize + move" commands, but when moving 
start point a get this error:

   (parted) resize
   Partition number? 1
   Start?  [64s]?
   End?  [419425019s]? 419425018
   (parted) move
   Partition number? 1
   Start? 65
   End?  [419425019s]? 419425019
   Error: Can't move a partition onto itself.  Try using resize, perhaps?

Using fdisk 'b' command in expert mode ('move beginning of data in a
partition') works, but it doesn't move the file system.. thanks!!

Regards,

-- 
Santi Saez
http://woop.es

AFAIK, you cannot do what you are trying to do.  The point of file
system alignment is to lay down the tracks on the entire disk so they
align with the sector boundaries of the underlying device.  Once
everything is laid down and you have installed OS and written data,
all of those blocks are already misaligned.  You cannot move them
unless you do a complete system backup, reformat, then restore the
backup.

You might be able to fudge it by shrinking the partition down, then
moving it to the end of the disk, then moving it again, this time to
an aligned section of the disk.  I can't imagine how long that would
take, and is probably risky on a production system.  To try this you
would probably need at least half of the disk unused.

Unless you expect to see serious performance increases from this, it's
not worth it.  Chalk it up to learning and use that knowledge on your
next installs.  You should test out the process and performance gains
on a development system first.


On Fri, Oct 22, 2010 at 7:00 AM, Santi Saez <santisaez at woop.es>
wrote:
> Hi,
>
> NetApp support has suggested us aligning partitions to improve
> performance, in short: starting sector must be divisible by 8. How can I
> move the start point in a misaligned partition -in production, with
> ext3- under Linux?
>
> A screenshot with a misaligned (start=63s) and aligned (start=64s)
> partition is available at:
>
> ? ? ? ?http://filesocial.com/lkwvvn2
>
> (If anyone is interested in this topic, NetApp has a good document
> explaining performance issues in misaligned partitions: "Best
Practices
> for File System Alignment in Virtual Environments",
http://goo.gl/EkBw)
>
> I have tried using parted "resize + move" commands, but when
moving
> start point a get this error:
>
> ? (parted) resize
> ? Partition number? 1
> ? Start? ?[64s]?
> ? End? ?[419425019s]? 419425018
> ? (parted) move
> ? Partition number? 1
> ? Start? 65
> ? End? ?[419425019s]? 419425019
> ? Error: Can't move a partition onto itself. ?Try using resize,
perhaps?
>
> Using fdisk 'b' command in expert mode ('move beginning of data
in a
> partition') works, but it doesn't move the file system.. thanks!!
>
> Regards,
>
> --
> Santi Saez
> http://woop.es
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos
>