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| -rw-r--r-- | DOCUMENTATION | 20 |
1 files changed, 17 insertions, 3 deletions
diff --git a/DOCUMENTATION b/DOCUMENTATION index 68288b0..fb435d1 100644 --- a/DOCUMENTATION +++ b/DOCUMENTATION @@ -21,9 +21,16 @@ Design: |-6/ <-- Saturday incremental |-7/ <-- Sunday incremental - seed.sfs is created from an initial backup and compressed using SquashFS. It - is then mounted, using a loopback device on ro/. Using aufs2, a union mount is - formed by ro/ and each of the numbered bins, each corresponding to a day. + seed.sfs is created from an initial backup and compressed using SquashFS, which i + is simply a filesystem which focuses on compression, but is read only. It's mounted, + using a loopback device, on ro/. Using aufs2, a union mount is formed by ro/ and each + of the numbered bins, each corresponding to a day. + + Wait, wat? What the heck IS a union mount? In simple terms, a union combines multiple + directories (which themselves could also be mount points) into a single resultant + mount point. Using our directory structure above as an example, each day (bin) is + overlayed (in order, its important) on the base (seed.sfs) to create what appears + to be an up to date backup in rw/. Skip the rest if you've had enough. At the time of the backup, the day is determined in order to prepare the union. If today is Thursday, `date +%u` returns 4. In order for rsync to properly create our @@ -41,3 +48,10 @@ Warnings: cause irrepairable damage to the union, rendering your incrementals worthless. +Further reading: + http://en.wikipedia.org/wiki/Aufs + http://en.wikipedia.org/wiki/UnionFS + http://aufs.sourceforge.net/ + http://en.wikipedia.org/wiki/SquashFS + http://en.wikipedia.org/wiki/Rsync + |