Re: [libvirt] libvirt and Parallels Cloud Storage

On Sun, Feb 10, 2013 at 02:20:02AM +0400, Alexander Gordeev wrote: > В Thu, 7 Feb 2013 16:09:31 +0000 > "Daniel P. Berrange" <berrange(a)redhat.com&gt; пишет: > > > > 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 > > If you are against changes in the XML maybe you are ok with a simpler > option: I create a storage backend for Pstorage, add two fields for > cache and io (or maybe just flags) to virStoragePoolTypeInfo and set > the right values for the new pool type. Then add some code to check > them to qemuBuildDriveStr (and to other drivers if possible, of course). > So no changes to XML and API. Is this better? No, the hypervisor drivers can only access data that is available via from the storage drivers via the XML or APIs. As I said before this is a policy decision for application authors to take, not for libvirt itself.