Am 31.05.2011 17:08, schrieb Gerardo Exequiel Pozzi: > On 05/31/2011 07:54 AM, Thomas Bächler wrote: >> Am 31.05.2011 03:21, schrieb Gerardo Exequiel Pozzi: >>> Hi >>> >>> * With 2.6.39 there is no aufs2 support, at least for a long time[#1]. >>> * I think that back in time with unionfs is not desirable, needs a >>> complete kernel patch. >>> * union-fs-fuse does not work good. >>> >>> What about using the method like in Fedora? (basically a device-mapper >>> with a snapshot in tmpfs). >>> >>> This change from file-to-file level to block-to-block logic. >> This actually sounds pretty cool. However, I don't understand how it >> works: The squashfs file system is a read-only one, how can we put that >> into a block-level snapshot? >> > Yes, but there are at least one downside: since is not an union-fs, > there is no concept of layers. We are currently using "overlay" thats > overlap some files on the layer "root-image".
This is not problematic. > About your question: The squasfs image contains only one file... an > image of and 4 GiB ext4. There is another small squasfs image with > another one file inside that is a "lvm snapshot". So dm device is made > via these images loopback mounted... Some of this doesn't make sense to me right now (especially the second squashfs image). However: With an ext4 loopback inside the squashfs image you loose one squashfs feature: metadata compression. I don't know how bad that will be though. I'll summarize what I think is going on: You mount the squashfs (loop0), and set up the ext4 image inside as loop1. You then create a large sparse file on tmpfs and set it up as loop2. Then, you create a snapshot device (can't use LVM here, can one use the device-mapper snapshot target directly?) with loop1 as read-only and loop2 as read-write layer. You then mount that device. Sounds doable, but not optimal (a VFS-based solution would be way cooler).
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