Hi, 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. This really gets messy and creates a management problem once many snapshots of a given origin are created, and gets worse with multiple origins. I am thinking, having a single device that would hold the cow blocks of any number of snapshots of a given origin (or more) would help solve this issue (Apart from this, having a single device helps share the cow blocks among snapshots very effectively in a variety of scenarios). But, it does require that LVM and EVMS be changed to suit this model and also makes the snapshot target quiet complex. I would like to receive some comments about what users, developers and others think about this. Thanks, Vijai P.S:- BTW, apologizes for cross posting. _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
