[linux-lvm] Re: [RFC] Multiple Snapshots - Manageability problem

Tomasz Chmielewski mangoo at wpkg.org
Thu Jan 24 11:02:52 UTC 2008

Dan Kegel schrieb:
> On Jan 23, 2008 8:16 AM, Tomasz Chmielewski <mangoo at wpkg.org> wrote:
>> Vijai Babu Madhavan, Thu, 11 Jan 2007 11:18:13 -0700, wrote:
>>> The problem of DM snapshots with multiple snapshots have been discussed
>>> in the lists quiet a bit (Most recently @
>>> https://www.redhat.com/archives/dm-devel/2006-October/msg00034.html).
>>> We are currently in the process of building a DM snapshot target that scales
>>> well with many snapshots (so that the changed blocks don't get copied to each
>>> snapshot). In this process, I would also like to validate an assumption.
>> Any news on that?
>> Still, with multiple snapshots write performance degrades linearly - is
>> any work done to change that anytime soon?
> Yes.  Dan Phillips has implemented a shared snapshot exception store.
> You can try it out now if you like; it's at http://zumastor.org.
> It feels a bit different from the user's point of view than LVM, though.
> It plays well with the device mapper and can be used with any
> block device (LVM or non-LVM).

Does it use device mapper (or it just "plays well with the device 
mapper")? Or is it a totally different technology?

I didn't find it explained very clearly in Zumastor HOWTO on 
http://zumastor.googlecode.com/svn/trunk/doc/zumastor-howto.html (other 
than pointers to /dev/mapper/zumatest, which probably means it uses 
device mapper).

Tomasz Chmielewski

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