Re: [Xen-users] SSD 4K Alignment?

[Adi Kriegisch <adi@xxxxxxxxxxxxxxx>]

Hey,

> Adi, just so I'm 100% clear on this. Are you saying that 4k aligned
> or not is irrelevant due to the 512 hard-coded issue with DomU? Is
> the performance hit you were seeing in your bug report still
> applicable to non RAID environments?
Those are two different issues:
You already have a file system that is aligned. On top of that there are
image files containing domU file systems. No need to do alignments here.
The issue I had was quite different: There was a RAID6 with 6 data disks
(instead of 4) and I also found some other issues with alignment. On top of
that there is what results from not passing through physical disk specs.

> Reason I ask is that with a
> single Windows 2008 R2 VM on XCP 1.6 all loaded on a Samsung 840
> 500GB SSD I am getting IOPS and transfer rates in IOMeter that are a
> fraction (as in 5%) of the manufacturers claims. I think I'll blow
> away my XCP install and put Windows 2008 R2 on directly and see what
> I get out of IOMeter there using the same testing profiles.
Pfff... there are many reasons that can happen. First and foremost did you
install pvgpl drivers and ensure they work?
IMHO using images isn't the fastest storage backend; but when using it, did
you give enough RAM to your Dom0? Did you disable balooning and pin CPUs
(there is more than one CPU attached to Dom0, right?)?

So I am pretty sure, your issue has nothing to do with 4K alignment. ;-)

-- Adi

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