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

On 2013-05-07 00:31, Adi Kriegisch wrote:

You mean in the context of using a file to contain the virtual disk
image? Just put it on a FS that is using 4KB sectors, and that is
aligned to a 4KB boundary, and when you are installing the guest
make sure you set up the FS to also use 4KB blocks.
Hmmm, that depends on what you do within the image: In case you create partitions within those images you need to assure that those partitions are aligned to use 4K blocks which boils down to using GPT for the partition
When you create a file system on the raw image you don't need to do
anything: the blocks are already aligned and it does not matter what
blocksize you use for creating the filesystem; so 512B is ok too.
I actually never used image files but only storage devices like lvm
volumes. But that depends on the use case, of course.

-- Adi

Xen-users mailing list

Thanks for the replies everyone.

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? 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.


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