[linux-lvm] logical volumes and raid alignment

[linux-lvm] logical volumes and raid alignment

[Alexander 'Leo' Bergolth]

Hi!

I am using LVM on a hardware RAID 5 and I'd like to tune the alignment
of lvm extents to match the raid stripe size.

My raid chunk size is 64k and I am using 5 data-bearing discs (raid 5
with 6 discs), so the raid stripe size should be 64k * 5 = 320k.

I have already managed to properly align the partition to a multiple of
this value and I am able to align the beginning of the first extent by
specifying --dataalignment 320k to pvcreate.

But unfortunately the --physicalextentsize must be a power of 2, so I
cannot use a multiple of 320k as the physical extent size.

What are your experiences with tuning and properly aligning lvm + raid?
Does anyone know a workaround?

Thanks,
--leo
-- 
e-mail   ::: Leo.Bergolth (at) wu.ac.at
fax      ::: +43-1-31336-906050
location ::: IT-Services | Vienna University of Economics | Austria

Re: [linux-lvm] logical volumes and raid alignment

[Stuart D. Gathman]

On Sun, 2 May 2010, Alexander 'Leo' Bergolth wrote:

> My raid chunk size is 64k and I am using 5 data-bearing discs (raid 5
> with 6 discs), so the raid stripe size should be 64k * 5 = 320k.
> 
> But unfortunately the --physicalextentsize must be a power of 2, so I
> cannot use a multiple of 320k as the physical extent size.
> 
> What are your experiences with tuning and properly aligning lvm + raid?
> Does anyone know a workaround?

Use 4 data bearing disks.  Let #6 be a spare.  You're supposed to have
a spare anyway.

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] logical volumes and raid alignment

[Luca Berra]

On Sun, May 02, 2010 at 10:33:03PM +0200, Alexander 'Leo' Bergolth wrote:
>Hi!
>
>I am using LVM on a hardware RAID 5 and I'd like to tune the alignment
>of lvm extents to match the raid stripe size.
>
>My raid chunk size is 64k and I am using 5 data-bearing discs (raid 5
>with 6 discs), so the raid stripe size should be 64k * 5 = 320k.
>
>I have already managed to properly align the partition to a multiple of
>this value and I am able to align the beginning of the first extent by
>specifying --dataalignment 320k to pvcreate.
>
>But unfortunately the --physicalextentsize must be a power of 2, so I
>cannot use a multiple of 320k as the physical extent size.
>
>What are your experiences with tuning and properly aligning lvm + raid?
>Does anyone know a workaround?
I had a similar issue, and best thing i came up with was creating volume
group with PE Size == chunk_size, and create/extend all logical volumes
to a multiple of data_disks PE.

L.

-- 
Luca Berra -- bluca@comedia.it
         Communication Media & Services S.r.l.
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