Re: [Qemu-devel] [RFC] qemu snapshot enchancement

[Wenchao Xia]

于 2013-1-28 21:38, Dietmar Maurer 写道:
> > If you've been using it for 4 years then it was without dm-thin, which is a new
> > snapshot mechanism that solves limitations of classic LVM snapshot
> > volumes.  So if you're referring to inefficient LVM snapshots then that should
> > be solvable now.
>
> Are you sure this work on shared iSCSI devices (I have my doubts)?
>
> Besides, we use RHEL6.3 kernel, and AFAIK dm-thin is still not marked stable 
> there.
>
> > 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.
  The solution seems OK in improving the performance, I just wondering
if it is possible to put it in lower level component, not qemu? It will
make qemu block layer more complicate, and since it can ignore the
format so it is more likely a storage dedicated function, so could
u check if it can be offloaded from qemu?

--
Best Regards

Wenchao Xia