> > Are you sure this work on shared iSCSI devices (I have my doubts)? > > If by "shared" you mean clustering support so multiple hosts can access > volumes from the same pool, then the answer is no.
Unfortunately this is the standard setup with our environment. > If by "shared" you mean that there are iSCSI devices which are attached to a > single host at a time but the mapping can change, then that should work fine. > > > Besides, we use RHEL6.3 kernel, and AFAIK dm-thin is still not marked > stable there. > > Yeah, it's still a fairly new feature. The key feature is that it uses a > single > storage pool which all snapshots share instead of the insane per-snapshot > volumes that need to be managed for classic LVM snapshots. > > > Or is LVM a pain for other reasons? > > > > a.) it only works on LVM (new solution works on any storage type) > > b.) You need free space on the VG (almost every user configures LVM > > without leaving any free space on the VG). > > c.) you need to specify snapshot size in advance > > d.) performance is bad on writes. > > > > The new solution work perfectly on all storage types, works on shared > > storage, and does not need any free space on the source storage. > > These are good points and it sounds like QEMU-level snapshots work great > for you. > > QEMU should support both our own snapshots as well as exploiting features > in lower levels of the storage stack. That way users can choose the best > option for their use case. Sure.
