1. MojaveFS Lookup Vlad Dascalu, 351C3 – U.P. Bucharest vlad.dascalu@goobix.com Jason Hickey, Cristian Ţăpuş, David Noblet California Institute of Technology

2. MojaveFS – Distributed Filesystem The advantages of distributed filesystems over the classic approach: Redundancy (avoid down-time due to hardware failures) Scalability (constant performance due to the ability of adding new resources, dynamically) Adaptability (adjust the amount of replication based on the resources’ access patterns)

3. MojaveFS – Resource Replication Information is spread across k replicas For a given resource we must identify the machines on which it can be found (due to replication) Novel idea: we map the directories and the files in subdomains, and we use DNS in order to retrieve the associated IP addresses.

4. MojaveFS – Subdomain Mappings / (filesystem root) becomes mojave-root. /dir1 becomes dir1.mojave-root. /dir1/dir2 becomes dir2.dir1.mojave-root. /dir1/dir2/dir3 becomes dir3.dir2.dir1.mojave-root.

5. MojaveFS – DNS Advantages Scalability and stability due to the usage of already-proven DNS technology at large-scale Internet scenarios Already existing mechanisms for information replication between master and slaves (DNS zone transfer) Libraries and tools for querying / configuring the DNS The availability of the bind server, which is open-source and under active development (sponsored by the Internet Software Consortium)

6. MojaveFS – Bind Interfacing There are 3 available APIs: BIND 9's Full function API BIND 9's SDB API BIND-DLZ API No API is able to provide the features required in order to be used for interfacing MojaveFS with Bind (incompatibility with the recent versions of Bind, security holes, lack of features) The solution: direct manipulation of the zone files

7. MojaveFS – Interfacing with OCaml The filesystem is written in the OCaml language The interface is achieved at two levels Interrogation interface for finding the IPs associated with specified resources Management interface for modification of the IPs Add a new resource (file/directory) Edit a resource Remove a resource

8. MojaveFS – Interrogation Interface There isn’t any portable OCaml code for network functions There are Unix command line tools specialized in querying the DNS Examples: host, dig, nslookup Large-scale availability of those tools in the most Linux distributions Solution: an OCaml library which launches one of those tools from the command line and parses their output in OCaml data structures.

9. MojaveFS – IPs Management Manipulate data structures in memory by using the Hashtbl interface Save and restore the data structures by using OCaml marshalling Use specific function for dumping the memory data structures in specific BIND zone files Avoid in this way to write a parser for reading the BIND zone files directly

10. MojaveFS – IPs Management (2) addEntry entry ip (bind the specified ip to the given resource) removeEntry entry (remove the specified resource from the directory hierarchy) updateTTL entry newTTL (control the maximum expiration time of any given cache copy)

11. MojaveFS - Conclusion DNS Lookup – a novel idea which uses an already existing layer of Internet infrastructure in order to implement scalability and redundancy in a distributed file-system More information: http://mojave.caltech.edu http://mojave.caltech.edu