Similar to #10775 for fewer memory allocations, since we use getOnlineDisks() extensively for listing we should optimize it further. Additionally, remove all unused walkers from the storage layer
File Info decoding, in particular, is showing up as a major allocator and time consumer for internode data transfers Switch to message pack for cross-server transfers: ``` MSGP: Size: 945 bytes BenchmarkEncodeFileInfoMsgp-32 1558444 866 ns/op 1.16 MB/s 0 B/op 0 allocs/op BenchmarkDecodeFileInfoMsgp-32 479968 2487 ns/op 0.40 MB/s 848 B/op 18 allocs/op GOB: Size: 1409 bytes BenchmarkEncodeFileInfoGOB-32 333339 3237 ns/op 0.31 MB/s 576 B/op 19 allocs/op BenchmarkDecodeFileInfoGOB-32 20869 57837 ns/op 0.02 MB/s 16439 B/op 428 allocs/op ```
