On Thu, 12 Oct 2017 15:32:24 +0100 Chris Murphy <lists@xxxxxxxxxxxxxxxxx> wrote: > On Thu, Oct 12, 2017 at 2:20 PM, Joseph Dunn <jdunn14@xxxxxxxxx> wrote: > > > > On Thu, 12 Oct 2017 12:18:01 +0800 > > Anand Jain <anand.jain@xxxxxxxxxx> wrote: > > > > > On 10/12/2017 08:47 AM, Joseph Dunn wrote: > > > > After seeing how btrfs seeds work I wondered if it was possible to push > > > > specific files from the seed to the rw device. I know that removing > > > > the seed device will flush all the contents over to the rw device, but > > > > what about flushing individual files on demand? > > > > > > > > I found that opening a file, reading the contents, seeking back to 0, > > > > and writing out the contents does what I want, but I was hoping for a > > > > bit less of a hack. > > > > > > > > Is there maybe an ioctl or something else that might trigger a similar > > > > action? > > > > > > You mean to say - seed-device delete to trigger copy of only the > > > specified or the modified files only, instead of whole of seed-device ? > > > What's the use case around this ? > > > > > > > Not quite. While the seed device is still connected I would like to > > force some files over to the rw device. The use case is basically a > > much slower link to a seed device holding significantly more data than > > we currently need. An example would be a slower iscsi link to the seed > > device and a local rw ssd. I would like fast access to a certain subset > > of files, likely larger than the memory cache will accommodate. If at > > a later time I want to discard the image as a whole I could unmount the > > file system or if I want a full local copy I could delete the > > seed-device to sync the fs. In the mean time I would have access to > > all the files, with some slower (iscsi) and some faster (ssd) and the > > ability to pick which ones are in the faster group at the cost of one > > content transfer. > > > Multiple seeds? > > Seed A has everything, is remote. Create sprout B also remotely, > deleting the things you don't absolutely need, then make it a seed. > Now via iSCSI you can mount both A and B seeds. Add local rw sprout C > to seed B, then delete B to move files to fast local storage. > Interesting thought. I haven't tried working with multiple seeds but I'll see what that can do. I will say that this approach would require more pre-planning meaning that the choice of fast files could not be made based on current access patterns to tasks at hand. This might make sense for a core set of files, but it doesn't quite solve the whole problem. -Joseph > > > -- > Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
