Caching

Andrew Security Andrew Scale and Performance Sprite Performance

Andrew File System

Sprite

Network File System

Andrew File System AFS, AFS2, Coda 1983 to present, Satya its champion Ideas spread to other systems, NT

Security Terms Release, Modification, Denial of Service Mutual suspicion, Modification, Conservation, Confinement, Initialization Identification, Authentication, Privacy, Nonrepudiation

System Components Vice Secure Servers Virtue Protected Workstations Venus Virtual File System Authentication Server

Andrew Encryption DES - Private Keys E[msg,key], D[msg,key] Local copy of secret key Exchange of keys doesn’t scale –Web of trust extends to lots of servers –Pair wise keys unwieldy

Andrew Authentication Username sent in the clear Random number exchange –E[X,key] sent to server (Vice) –D[E[X,key],key] = X –E[X+1,key] to client (Venus) BIND exchanges session keys

Authentication Tokens Description of the user ID, timestamp valid/invalid Used to coordinate what should be available from Vice (server) to Virtue (client)

Access Control Hierarchical groups –Project/shared accounts discouraged Positive/Negative Rights U(+) — U(-) VMS linear list & rights IDs Prolog engine in NT Netware has better admin feedback

Resource Usage Network not an issue –Distributed DOS ‘hard’ Server High Water Mark –Violations by SU programs tolerated –Daemon processes given ‘stem’ accnt Workstations not an issue –User files in Vice

Other Security Issues XOR for session encryption PC support via special server Diskless workstations avoided

Enhancements Cells (NT Domains) Kerberos Protection Server for user administration

Sprite Components Client Server Local Disk Server Disk Client CacheServer Cache

Sprite Design Cache in client and server RAM Kernel file system modification –Affects system/paging and user files Cache size negotiated with VM Delayed 30s write-back –Called ‘laissez-faire’ by Andrew

NFS Comparison Presumed optimized RPC access semantics –NFS uses UDP, others TCP Sprite targeting 100+ nodes Andrew targeting 5,000+ nodes

Andrew Scale and Performance Dedicated server process per client Directory redirection for content Whole file copy in cache

Problems already… Context switching in server TCP connection overhead –Session done by kernel Painful to move parts of VFS to other servers –Volume abstraction fixed this later

Cache Management Write on close No concurrent write Versioning User level Delayed write Cache disabled Versioning Kernel level

Function Distribution TestAuth - validate cache GetFileStat - file status Fetch - server to client Store - client to server 61.7% 26.8% 4.0% 2.1%

Performance Improvements Virtue caches directory Local copy assumed correct File id’s, not names, exchanged Lightweight Processes (LWP) –Context data record on server

Andrew Benchmarks

Sprite Throughput

Sprite Benchmarks

Cache Impact - Client

Cache Impact - Server

Cache Impact - Net

Comparison

General Considerations 17-20% slower than local Server bottleneck Scan for files and read almost all local 6-8x faster vs no cache Server cache extends local cache Remote paging fast as local disk! 5x users/server

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