NeST: Network Storage Technologies Building an I/O Appliance on Commodity Systems John Bent, Remzi Arpaci-Dusseau and Miron Livny www.nestproject.com

Problem Statement Appliances are attractive because they are robust, reliable, available and especially because they are easy to use. To fulfill these criteria, traditional network appliances impose policy decisions on their users and are built either as kernel modules or upon specially designed kernels. “How to build a portable, configurable I/O appliance?”

Goals Provide stable, robust and easy to use network storage on a variety of platforms Allow configuration of server modules to fit application needs Maintain high server throughput under heavy load Degrade client performance gracefully as concurrency increases

Concurrency Architectures Nest Structure Protocols Name Space Static Configuration Administrative Interface Concurrency Architectures Runtime Adaptation Storage Management Consistency Semantics

Protocols Nest currently supports the following client requests in “nest-speak”: Send/receive file Send/receive partial file Query statistics Directory operations Remove file Timestamp request Future support: ftp, http, nfs, WiND fs.

Concurrency Architectures Non-blocking single process (NOB) Pre-allocated pool of processes (POP) Pre-allocated pool of threads (POT) All concurrency architectures use one control thread to accept and dispatch client requests. This approach will more easily allow centralized decision making as regards admission control, authentication and quality of services guarantees.

Other Modules Static configuration Namespace Runtime adaptation Build the most appropriate I/O appliance based on knowledge of the host system and the application needs Namespace Current: flat namespace Future: hierarchical Runtime adaptation Bandwidth monitoring and other flows of information may prove useful in consistently maximizing system throughput

Even More Modules Consistency semantics Storage management Well defined behavior is necessary in order to allow concurrent client access to the same file Storage management Current: ext2 FS on linux Future: raw disk management Administrative interface An “easy to use” tool must have a nice administrative interface. This will probably be added through the http protocol.

Performance Server bandwidth in each of the concurrency architectures remains constant as the number of clients increases. Client latency and bandwidth are also affected correctly as client concurrency grows.

Future Future Work Future Applications Quality of service Admission control, authentication Hybrid concurrency architectures Static configuration, runtime adaptation, namespacing, storage management, consistency semantics Future Applications Condor checkpoint server Local staging area for Condor jobs which have flocked over the WAN Storage “brick” for WiND Lots and lots and lots and lots more