A round-robin FUSE passthrough filesystem. Based on passfs but tweaked to support multiple roots.
Imagine you have 4 NFS servers sharing out the same clustered filesystem. Due to CPU or other resource limitations each NFS server can only serve out content at 2.5 Gbit/s.
There's a multi-threaded client application which wants to read from the NFS filesystem at 10 Gbit/s. You can mount up each NFS server under four different mount points but then how do you get the application to read from all of them at once without modifying it?
$ ./make.sh
$ mkdir /robin /nfs1 /nfs2 /nfs3 /nfs4
$ mount -o ro nfs-server-1:/shared /nfs1
$ mount -o ro nfs-server-2:/shared /nfs2
$ mount -o ro nfs-server-3:/shared /nfs3
$ mount -o ro nfs-server-4:/shared /nfs4
$ ./robinfs /robin /nfs1 /nfs2 /nfs3 /nfs4
$ cd /robin; ls -l
lrwxrwxrwx 1 root bin 64 Dec 16 2003 file1 -> /nfs4/file1
lrwxrwxrwx 1 root bin 63 Dec 16 2003 file2 -> /nfs2/file2
lrwxrwxrwx 1 root bin 64 Dec 16 2003 file3 -> /nfs3/file3
lrwxrwxrwx 1 root bin 63 Dec 16 2003 file4 -> /nfs1/file4
If you want to expose the contents as regular files rather than symlinks use the -p flag. This will incur a significant CPU cost as all data must be copied back and forth to userspace.
- Filesystems should have identical content
- Will not improve single-stream performance, each file handle is only associated with a single backend
- Writing might work but is untested, my use case is read-only
- Only tested under FUSE 2.9.2
- Mapping is not persistent (open a file multiple times and you'll get different backends), not great for caching