Remote Files Traditional Memory Interfaces Process Primary Memory - PowerPoint PPT Presentation

Remote Files

Traditional Memory Interfaces Process Primary Memory Interface Secondary Memory Interface Virtual File Memory Management Device Interface Physical Storage Memory Devices

Explicit File Copying ¥ Need a way for a process on one machine to pass info to a process on another machine ¥ Technique Ð Sender writes a file Ð User manually copies file to a remote machine Ð Receiver opens the file and reads it ¥ Very coarse grained ¥ Very high latency

Multics Segmented Memory Process Primary Memory Interface Secondary Memory Interface Segmented File Virtual Management Memory Device Interface Physical Storage Memory Devices Normal data flow Alternative data flow

Remote Secondary Memory Process Secondary Memory Interface File Management Client Interface to Remote Store Device Interface Storage Comm Devices Network

Refined View Client Machine Process Secondary Memory Interface File Management Server Machine Remote Remote Access Secondary Storage Storage Comm Storage Devices Network Devices

Refined View Client Machine ¥Server is a remote disk Process ¥Client & server implement file manager Secondary Memory Interface ¥Replicate file mgrs, then copy files File Management Server Machine Remote Remote Access Secondary Storage Storage Comm Storage Devices Network Devices

Remote Disk Server file mgr: diskRequest(details); VDD: Pack parameters; VDD: Send request; (wait for response) Client Machine General File Management Server Machine Virtual Remote Disk Driver Disk Application Storage Comm Storage Devices Network Devices

Remote Disk Server file mgr: diskRequest(details); VDD: Pack parameters; (waiting for a request) VDD: Send request; RDA: Unpack parameters; (wait for response) RDA: Generate local disk request; (waiting) RDA: Generate reply; RDA: Send reply Client Machine (waiting for a request) General File Management Server Machine Virtual Remote Disk Driver Disk Application Storage Comm Storage Devices Network Devices

Remote Disk Server file mgr: diskRequest(details); VDD: Pack parameters; (waiting for a request) VDD: Send request; RDA: Unpack parameters; (wait for response) RDA: Generate local disk request; (waiting) VDD: Receive reply; RDA: Generate reply; VDD: Unpack parameters; RDA: Send reply Client Machine VDD: Return to file mgr (waiting for a request) General File Management Server Machine Virtual Remote Disk Driver Disk Application Storage Comm Storage Devices Network Devices

Performance & Reliability ¥ Became commercially feasible in about 1986 ¥ Biggest concern was reliability Ð Reliable command execution ¥ Time-outs ¥ Idempotent disk operations Ð Crash recovery ¥ Stateless servers ¥ Forerunner of the Ònetwork computerÓ

Remote File Server ¥Read/write management ¥Block management ¥Pack/unpack byte stream ¥Buffering ¥Buffering ¥Device management ¥... ¥... Client Machine General File Management Server Machine Client Part of Server Part of Remote File System Remote File System Storage Comm Storage Devices Network Devices

Block Caching ¥ Widely used in all file systems ¥ In RFS can buffer at: Ð Server ¥ DoesnÕt avoid network latency Ð Client ¥ Consistency ¥ Sometimes use sequential write consistency (no sharing if there are multiple writers)

Crash Recovery ¥ Client has a file open and server crashes Ð Distributed state makes recovery difficult Ð Can counteract with a stateless server Ð But it requires that state be transmitted with every service request ¥ Recovery-oriented file service, e.g., Sun NFS ¥ Performance-oriented file service

Directories ¥ Names Ð Superpath names Ð Remote mount ¥ Opening a file