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Re: [dm-devel] Shared snapshots




On Mon, 11 Jan 2010, Pasi Kärkkäinen wrote:

> On Mon, Jan 11, 2010 at 04:12:43AM -0500, Mikulas Patocka wrote:
> > 
> > 
> > On Thu, 7 Jan 2010, Pasi Kärkkäinen wrote:
> > 
> > > On Wed, Jan 06, 2010 at 09:38:00AM -0500, Mikulas Patocka wrote:
> > > > Hi
> > > > 
> > > > I uploaded new code for shared snapshots at
> > > > http://people.redhat.com/mpatocka/patches/kernel/new-snapshots/devel/
> > > > 
> > > > Changes:
> > > > - two queues, one for reads and one for writes, to improve read latency 
> > > > when the device is write-congested
> > > > - limit number of reallocations in flight (VM subsystem sends all writes 
> > > > at once and without limit it creates big lags).
> > > > - fixed one place where it didn't handle on-disk errors
> > > > - simplified bitmap creation, removed some unneeded code
> > > > - new macro for error reporting, as suggested by Zdenek
> > > > - some comments added
> > > > - DM_ prefix added to some macros
> > > > 
> > > > Userspace for lvm 2.02.53 is at
> > > > http://people.redhat.com/mpatocka/patches/userspace/new-snapshots/lvm-2.02.54/
> > > > 
> > > > Please, someone, do offensive testing with this --- i.e. apply the 
> > > > patches, try it, and try all possible lvm commands with it, try to stress 
> > > > and crash it in various ways, etc. If we wait with testing until Alasdair 
> > > > reads the code, it won't get much testing...
> > > > 
> > > 
> > > Sorry for a stupid question, but what does "shared" mean? Support for CLVM?
> > > 
> > > -- Pasi
> > 
> > No, it is not clustered.
> >
> 
> Ok. Do you know if there has been work making snapshots work with CLVM? 
> 
> I remember there was some patches earlier, but no idea about the status
> of those..

There is kernel support, see 
http://people.redhat.com/mpatocka/patches/kernel/all/series.html (the last 
section, "Mikulas' clustering"). The patches are old, they may need 
conflict resolving.

But there is no userspace support. So, if you set it up manually with 
dmsetup and pass it a correct locking ID, it may work.

Mikulas

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