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.. > It means that you can create more snapshots (actually 2^32), they have a > common snapshot store and data in this store are shared. > > Normal snapshots get extremely ineffective when using multiple snapshots > --- for example, if you have 10 snapshots, data have to be written 10 > times and any writes to the origin are 10 times slower. Shared snapshots > write data only once. > > A possible use for them is to take periodic snapshot, for example once per > 5 minutes, to record system activity. > > Another possible use is to create one master image with system image and > take many snapshots, each snapshot for one virtual machine. > This sounds excellent! Thanks for explaining. -- Pasi -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
