On Tue, Jan 17, 2012 at 10:59:30AM -0500, Ted Ts'o wrote: > On Tue, Jan 17, 2012 at 10:13:31AM +0000, Joe Thornber wrote: > > iii) We add support to patch metadata changes into the running > > metadata device. This would allow us to map the origin directly into > > the pools data device (eg, using a linear target). And then introduce > > a mapping for that origin. This would mean the origin would appear as > > a thin dev within the pool. > > Have you considered just doing this part first? If there's a way that > an existing linear region could be considered a data source for a > pool, then wouldn't you get full support of existing LVM2 volumes > (read-only and read/write) for free, at one fell swoop? Yes, this is the solution that I like best. But I've only recently thought of it whilst I coded up the thinp_dump and thin_restore tools. Note that by using these tools and doing some manipulation of the metadata you can do this today in an offline mode. > Given that it's relatively rare that volume groups get moved, this > could even be something which is done as a off-line conversion step so > that existing LVM volumes are treated as "thin-provisioned voumes" > that happened to be fully provisioned, with some flag so that a > discard operation doesn't cause the blocks to be freed for use by some > other thin-provisioned volume, but instead is propagated down to the > hardware (for better SSD performance). Certainly the discard support needs to do two things; release the block and pass the discard down to the device. Making the first part optional sounds sensible to me. - Joe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
