Wow! Impressing. This will make history!
If this is possible, than we are able to implement a solution, which can do: - progressive block level incremental forever (always incremental on block level : this already exist) - instant recovery to point in time (using the mentioned methods you just described) For example, lets say that a client wants to restore a file system, or a logical volume to how it looked a like yesterday. Eventhough there are no snapshot, nor any data. Than the client (with some coding); can start from an empty volume, and re-attach a cow device, and convert that using lvconvert --merge, so that the copying can be done in background using the backup server. If you forget about "how we will re-create the cow device"; and just focusing on the LVM ideas of re-attaching a cow device. Do you think that I have understood it correctly? Den tors 24 okt. 2019 kl 18:01 skrev Zdenek Kabelac <zkabe...@redhat.com>: > Dne 23. 10. 19 v 13:24 Tomas Dalebjörk napsal(a): > > I have tested FusionIO together with old thick snapshots. > > I created the thick snapshot on a separate old traditional SATA drive, > just to > > check if that could be used as a snapshot target for high performance > disks; > > like a Fusion IO card. > > For those who doesn't know about FusionIO; they can deal with > 150-250,000 IOPS. > > > > And to be honest, I couldn't bottle neck the SATA disk I used as a thick > > snapshot target. > > The reason for why is simple: > > - thick snapshots uses sequential write techniques > > > > If I would have been using thin snapshots, than the writes would most > likely > > be more randomized on disk, which would have required more spindles to > coop > > with this. > > > > Anyhow; > > I am still eager to hear how to use an external device to import > snapshots. > > And when I say "import"; I am not talking about copyback, more to use to > read > > data from. > > Format of 'on-disk' snapshot metadata for old snapshot is trivial - being > some > header + pairs of dataoffset-TO-FROM - I think googling will reveal couple > python tools playing with it. > > You can add pre-created COW image to LV with lvconvert --snapshot > and to avoid 'zeroing' metadata use option -Zn > (BTW in the same way you can detach snapshot from LV with --splitsnapshot > so > you can look how the metadata looks like...) > > Although it's pretty unusual why would anyone create first the COW image > with > all the special layout and then merge it to LV - instead of directly > merging... There is only the 'little' advantage of minimizing 'offline' > time > of such device (and it's the reason why --split exists). > > Regards > > Zdenek > > >
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