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Re: [linux-lvm] ext3 on lvm2 on raid10



On Fri, 27 Feb 2009 10:13:31 +0100
Milan Broz <mbroz redhat com> wrote:

> Daniel Iliev wrote:
> > How is the raid10 chunk size related to LVM2 layout and how do
> > ext3's "stride" and "stripe-width" parameters depend on LVM2?
> > 

--snip--
> 
> Hi,
> 
> lvm2 since version 2.02.41 allows automatically align LV start
> according to underlying md device "chunk" size.
> 
> See this paramater in lvm.conf:
>     # By default, if a PV is placed directly upon an md device, LVM2
>     # will align its data blocks with the the chunk_size exposed in
> sysfs. # 1 enables; 0 disables.
>     md_chunk_alignment = 1
> 
> You should also set extent size as multiple of chunk size.
> 
> (The development code in CVS also allows set the alignment manually
> using parameter, so administrator can set the align value according
> to other types of underlaying devices - useful for hw raid, SSD, etc.)
> 
> Milan
> --
> mbroz redhat com
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm redhat com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> 


Thank you!

I need a little more clarification, though.

1) Does the "2 far copies" raid10 layout matter? I'd prefer it,
because my tests showed much better performance with it, but there was
no LVM


2) How about the ext3 params
I mean what if I create raid and LVM like this:

mdadm --create /dev/md1 --raid-devices=4 --level=10 --layout=f2 \
--bitmap=internal --chunk=1024 /dev/sd[a-d]2

pvcreate /dev/md1

lgcreate vg00 /dev/md1
 # ^^^ PE size would be 4MB by default, 4x chunksize in this case,
 right?

lvcreate -L100G -n home vg00
 # ^^^ should I use --stripes and --stripesize here?

mkfs.ext3 -E stride=X,stripe-width=Y /dev/lv00/home

Now what should X and Y be?

 stride:
 1024 [raid chunk in KBytes] * 1024 [bytes] / 4096 [ext3 block in Bytes]
 stride = 256

 stripe-width:
 256 [stride-size] * 2  [nr data disks] = 512
 stripe-width = 512

    OR

 4 [LVM PE in MBytes] * 1024*1024 [bytes] / 4096 [ext block in bytes] 
 stride = 1024

 stripe-width:
 1024 [stride-size] * 2  [nr data disks]
 stripe-width = 2048



-- 
Best regards,
Daniel


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