Hello Dale,
Dale Dude:
> Can aufs be used in its current form, or be modified to do so, to join a
> number of file systems, as it already does, but if writing to a full rw
> branch it will detect this and start writing to another rw branch? Or
> possible round robin all file "creates" to all rw branches?
Currently aufs doesn't have such feature. How about these workarounds
for that feature?
(I didn't try them actually)
1. LVM or RAID
I think it is most suitable or appropriate.
2. rotate writable branches by yourself
# mount -t aufs br:/rw1:/rw2:/ro none /aufs
(/rw2 is readonly branch by default)
when /rw1 becomes full, then rotate the branch.
# mount -o remount,del:/rw2:prepend:/rw2:mod:/rw1=ro /aufs
or
# mount -o remount,mod:/rw2=rw,del:/rw1:ins:1:/rw1 /aufs
cautions or expectable problems
- /rw2 (or /rw1) must not be busy since it is deleted once
- the logically removed entries may appear, since they may exist on /rw2
3. create or move the parent directory betwee the branches
when you create a file, aufs decides the branch like this,
- find the existing parent directory.
- when the topmost parent dir exists on a readonly branch, it will be
copied-up. and the file will be created under the copied-up dir.
- when the topmost parent dir exists on a writable branch, the file
will be created on that branch.
so if you create or move the parent directory before you create a
file, you will be able to decide which branch to be used.
cautions or expectable problems
- you need to specify udba=inotify aufs mount option.
- you may have to take care the whiteouts on the upper branch.
> If its currently not possible, what would be someones thoughts on
> modifying aufs to do this? To hard, impossible, wont work because of <X>?
I have (or had) a plan to introduce a new policy to decide the
branch. The policy is mainly for performance, not a feature as you
wrote. But once the branch policy is implemented, it may be easier to
implement such feature. When I have time, I will try.
But don't expect me too much. :-)
Junjiro Okajima
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