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Re: [libvirt] libvirt and Parallels Cloud Storage



On Mon, Feb 04, 2013 at 08:13:20PM +0400, Alexander Gordeev wrote:
> Hi!
> 
> I'd like to develop libvirt integration with Parallels Cloud
> Storage (Pstorage) which is a new distributed file system from
> Parallels designed specifically for storing VM images:
> http://www.parallels.com/products/pcs/cloud-storage/

Yay, yet another filesystem :-( Everyone seems to think they need to
write their own custom network/cluster/cloud FUSE filesystem these
days.

> It's not a POSIX FS but there is a FUSE client for it that can be
> used to access and manipulate images. It's quite high speed but only
> when used with O_DIRECT + aio. I tried to setup several KVMs on top of
> a Pstorage mount using virt-manager. It worked good, but I had to:
> 1. tune cache and IO settings for every disk
> 2. disable space allocation by libvirt because it is using sync IO and
> is therefore slow
> 
> I tried to find ways to solve the first issue and IMHO this can be
> done by adding a way to specify per-pool defaults for cache and IO
> settings. I didn't find any way for this in the current code and UI.
> I'd like to add a new storage backend also that will be a 'dir' backend
> with extra ability to manage Pstorage mount points and UI integration.
> I'd like to merge my work to the main tree when it's finished if
> possible.

I don't think that putting cache/IO defaults in the XML is really
appropriate. There are too many different scenarios which want
different settings to be able to clearly identify one set of
perfect settings. I see this as primarily a documentation problem.
Someone needs to write something describing the diferrent settings
for each storage pool & what the pros/cons are for each. Downstream
app developers can then make decisions about suitable defaults for
their use cases


Daniel
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