CentOS - Apr 2011 - 4kB sector size HDDs

Hello again.

Do any of you have one of the 'new' HDDs with 4kB Sectors currently in
use?
I would upgrade to the 4kB disks but I don't know if this might be
problematic as I intend to use ZFS w/ RAIDz or at least a classic RAID6.
How might this affect performance under 5.5 and how do I go about setting up
the alignment of the partitions I use?

Kind regards

Dawid Horace

> how do I go about setting up
>the alignment of the partitions I use?

If you use one large partition it's easy: you just create the partition
leaving 1 meg of free space before the partition. This causes the partition
to start at sector 2048, which is a number that 4096 is divisible by. Newer
versions of disk utilities like gparted suggest this for you by placing a 1
in the 'Free Space Preceding' box when you go to create a new partition.

If you create multiple partitions, it's a little harder since you have make
sure that subsequent partitions start on sectors that can be divided evenly
into 4096. I've never done this as I always set up one large partition on my
storage arrays, and I use a separate drive for the OS to boot from and
another separate drive for my VMs. I do this for performance reasons.

All of this is explained more or less if you google.

--On Thursday, April 21, 2011 11:16:36 AM +0200 Dawid Horacio Golebiewski
<dawid.golebiewski at tu-harburg.de> wrote:
> Do any of you have one of the 'new' HDDs with 4kB Sectors currently
in
> use?
I have them in use, and set up the partitions manually before installing
the OS.  This is the relevent entry from my server changelog, prior to
installing CentOS 5.5:

    + since this machine is using new drives with 4k blocks,
      used fdisk to ensure that sector alignment will be sane:

        fdisk -H 224 -S 56 /dev/sd{a,b} 

      In doing so, I created a 200MB RAID1 partition (type 0xfd)
      and another RAID1 partition with the remaining disk for use
      by LVM.

      I found it necessary to use fdisk manually on both disks,
      because the following command choked (probably due to
      the geometry thing):

        sfdisk -d /dev/sda | sfdisk /dev/sdb
        (DOESN'T WORK)

I case it's not obvious, the partitions on sda and sdb are then
mirrored, the small one for /boot, the large one for the remaining
filesystems under LVM.

If you're using the Caviar green drives, beware of excessive head
park and quickly increasing load cycle counts.  I fixed that with
using an idle timeout of 300 seconds (vice 8 seconds) per:


<http://community.wdc.com/t5/Desktop/Green-Caviar-High-Load-Cycle-Cout-after-short-operation-time/td-p/15731/page/7>

Devin