Multiple Snapshots - Manageability problem
Quoted 9 lines · 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.
Today, when a single snapshot gets created, a new cow device of a given size is also created. IMO, there are two problems with this approach:
a) It is difficult to predict the size of the cow device, which requires a prediction of the number of writes would go into the origin volume during the snapshot life cycle. It is difficult to get this prediction right, as very high value reduces utilization and low value increases the chances of snapshot becoming full.
b) A new cow device needs to be created every time.
Hi,
Any news on that?
Still, with multiple snapshots write performance degrades linearly - is any work done to change that anytime soon?
Signature · 8 lines
Tomasz Chmielewski http://wpkg.org _______________________________________________ linux-lvm mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
Quoted 6 lines · Tomasz Chmielewski
Quoted 4 lines · 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).
Quoted 8 lines
Quoted 3 lines
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).
- Dan
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Quoted 12 lines · Dan Kegel
Quoted 11 lines · Tomasz Chmielewski
Quoted 7 lines · 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?
Quoted 8 lines
Quoted 2 lines
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).
Signature · 8 lines
Tomasz Chmielewski http://wpkg.org _______________________________________________ linux-lvm mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
Quoted 9 lines · Tomasz Chmielewski
Quoted 5 lines · Dan Kegel
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?
It is a device mapper target, so yeah, it uses device mapper.
Quoted 4 lines
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).
A little further down the page, http://zumastor.org links to
http://zumastor.googlecode.com/svn/trunk/doc/desimplnotes.html
which does mention it explicitly.
- Dan