Comment 15 for bug 943119

Tim,

Thank you for the quick answer.
I believe the main reason is that the documentation is basically absent for overlayfs. I spent a lot of time trying to find some but I've only found bits and pieces mainly describing at a general level how it works.
I doubt that it can give me the level of control that aufs is giving me.

I had 6 hard drives (a total of 11 TB of storage space) in my desktop computer (on Ubuntu 11.10) with multimedia content on them stored in a top level folder called multimedia on each drive (all 6 drives have only one partition each). Inside multimedia I have from 1 to 6 subfolders holding different categories of multimedia files depending on the source disk. Besides the multimedia top folder there are some other folders holding various data. I was using AUFS to aggregate all 6 mounting point folders (from /media) in a single merged folder called BFD through this line in fstab:

none /media/BFD aufs br:/media/2TB_1=rw,br:/media/2TB_2=rw,br:/media/2TB_3=rw,br:/media/2TB_4=rw,br:/media/1.5TB_1=rw,br:/media/1.5TB_2=rw,create=tdp,sum 0 0

The policies gave me the liberty to control the behavior of AUFS exactly the way I wanted and that is: new files that are copied on BFD in a folder that originated from one of the drives to be created and stored on the same drive not not on the first writable branch with enough space available on it. I have an application that manages most of the multimedia content of BFD and while for read only access I guess any stackable unification filesystem would be be ok, but for writing, I've found that only aufs was suitable. I've also used to use mhddfs, but that one runs in userspace and on the other hand does not have the policies system so it would always write on the first drive with enough free space.

So I've decided to move the 6 drives in a dedicated NAS box and implement the same mechanism that proved to be the best suitable for what I need. Once I've installed Ubuntu server 12.04 and I've moved all the drives phisically inside the NAS I attempted to re-created BFD with aufs and this was the point where I've encountered the absence of aufs support (through an error that lead me to an open bug, mentioned in this bug's description)