On Wed, Jul 6, 2016 at 2:27 PM, Nir Soffer <nsoffer@redhat.com> wrote:

On Wed, Jul 6, 2016 at 12:18 AM, David Twersky <dmtwersky@gmail.com> wrote:
> We use a lot of flash arrays, and some of them require that devices be 4k
> aligned, is it possible to create a Fibre Channel Storage Domain and have it
> 4k aligned?

Is it required or preferred? Because while most of our data is 4K aligned, some writes aren't - mainly metadata of the storage domain.

So you won't be usually suffering from mis-aligned writes (or reads) which are costly, but we must be able to perform atomic 512b writes (which may translate to a read-modify-write of course in the flash).

I'm not sure what we expose to VMs, btw - if we can expose to them 4K drive...?

I don't think we support this.

Indeed - we assume sector size to be 512b in the code:

lib/vdsm/storage/constants.py:SECTOR_SIZE = 512

Can you use a direct LUN, though?

For example, we assume that writing 512 bytes blocks is atomic, if these
writes will fail because the minimal block is 4k, block storage metadata
operations will fail.

Anyway, why not try to add such lun and create a storage domain for testing?

Nir
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