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From: Jonathan de Boyne Pollard on 8 Feb 2010 23:44
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<blockquote
cite="mid:ccc1608c-df4b-4239-83aa-de517e845851(a)o28g2000yqh.googlegroups.com"
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<p>The server is running on VMware, [...] the .vmdk-files, [...] </p>
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<p>Then all of your considerations of performance gain due to partition
alignment go out of the window.&nbsp; Fiddling with the disk layout as seen
by the guest operating system is pretty pointless when you are using
"discs" that are in fact files, potentially fragmented and variously
aligned, on a host volume.&nbsp; You're reading all of the wrong
literature.&nbsp; All of the literature that you've been reading
pre-supposes <em>real</em> discs, not <em>virtual</em> ones.&nbsp; Go and
read the literature on disc I/O alignment in VMWare.<br>
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From: Björn Pettersson on 9 Feb 2010 09:42
On 9 Feb, 05:44, Jonathan de Boyne Pollard <J.deBoynePollard-
newsgro...(a)NTLWorld.COM> wrote:
> The server is running on VMware, [...] the .vmdk-files, [...]
>
> Then all of your considerations of performance gain due to partition alignment go out of the window.  Fiddling with the disk layout as seen by the guest operating system is pretty pointless when you are using "discs" that are in fact files, potentially fragmented and variously aligned, on a host volume.  You're reading all of the wrong literature.  All of the literature that you've been reading pre-supposesrealdiscs, notvirtualones.  Go and read the literature on disc I/O alignment in VMWare.

RCan,
Thanks for the link :) We're running on a Hitachi SAN, for which I
know the stripe unit size. We have a good relation with our SAN team.
I have read Jimmy May's ppt-deck, and I agree, he is the man. In fact,
I sent him a mail using the form on his blog, yesterday, but I bet he
is drowning in questions so my hopes on receiving an answer is quite
low.

Jonathan,
The example aligning dynamic disks in a virtual machine on Windows
2008 was using .vmdk-files, but I am pretty sure the same thing could
be done with raw LUN's (RDM). I have read about I/O alignment when
using VMware, and as far I know, as long as the VMFS volume is
aligned, there is nothing preventing me from gaining performance when
aligning the partition in the gust OS. VMware claims that the
performance impact running VMFS is on par with RDM. As for raw LUN's,
all I really need to care is to have the guest OS aligned correctly
with my SAN. Would I prefer to have the customer running MSSQL on a
physical box? Hell yes! But the customer does not want to migrate to a
physical platform atm, so there isn't really very much I can do to
increase disk performance except for partition alignment.

VMFS vs RDM
http://www.vmware.com/files/pdf/vmfs_rdm_perf.pdf

Partition Alignment on VMFS partitions
http://www.vmware.com/pdf/esx3_partition_align.pdf

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