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Old 04-21-2011, 09:16 AM
"Dawid Horacio Golebiewski"
 
Default 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

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Old 04-21-2011, 12:40 PM
"compdoc"
 
Default 4kB sector size HDDs

> 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.






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Old 04-21-2011, 03:17 PM
Devin Reade
 
Default 4kB sector size HDDs

--On Thursday, April 21, 2011 11:16:36 AM +0200 Dawid Horacio Golebiewski
<dawid.golebiewski@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

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