At Mon, 20 Jun 2011 16:46:18 -0400 CentOS mailing list <centos@xxxxxxxxxx> wrote:
>
> On Mon, Jun 20, 2011 at 09:32:03PM +0200, Markus Falb wrote:
> > On 20.6.2011 21:19, Stephen Harris wrote:
>
> > > LVM; pvcreate, vgcreate, lvcreate. What's a partition? :-)
> >
> > But your filesystem has still to be aligned correctly. Is lvm 4k
> > friendly ? Is md ?
>
> That is a very good question, and one of the underlying aspects of
> my original question :-)
>From 'man vgcreate':
-s, --physicalextentsize PhysicalExtentSize[bBsSkKmMgGtTpPeE]
Sets the physical extent size on physical volumes of this volume
group. A size suffix (k for kilobytes up to t for terabytes) is
optional, megabytes is the default if no suffix is present. The
default is 4 MB and it must be at least 1 KB and a power of 2.
This suggests that so long as the Volume Group is properly aligned and
the PE's are defined as a multiple of 4KB, logical volumes will be
properly aligned. At least that is how I read it.
>From 'man mdadm':
-c, --chunk=
Specify chunk size in kibibytes. The default is 64.
This also suggests that so long as the physical partitions are properly
aligned and so long as one does not specify something strange for this
option (eg something other than a multiple of 4), then the stripes in
the RAID array will be properly aligned. I would *guess* that using a
whole bare disk would be aligned (at LBA 0) and any partitions created
with a proper partitioning tool (GNU Parted) will be properly aligned.
>
>
--
Robert Heller -- 978-544-6933 / heller@xxxxxxxxxxxx
Deepwoods Software -- http://www.deepsoft.com/
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