enabling large-scale storage in sensor networks with the coffee file system ispn 2009 lawrence
TRANSCRIPT
Enabling Large-Scale Storage in Sensor Networks with the Coffee File
System
ISPN 2009Lawrence
Introduction
Motivation Existing storage systems access the flash
memory directly and ad hoc, or use too much RAM to handle large flash memories.
Storage abstractions
Meet the need for a generic, high speed, flash-based file system that is feasible for a wide rage of sensor devices.
Storage In Sensor Network
Storage Centricity From communication-centric to storage-
centric Batching data for saving energy Delay-tolerant v.s. delay-sensitive(ex.
fire alarm) Storage-centric sensor net require
storage facilities.
Storage In Sensor Network(Cont.)
Using Storage as Virtual Memory Use the flash as swap area. VM requires faster storage systems. Require storage manage application:
1. Wear leveling2. Garbage collection3. Space allocation
In this paper, there is a storage abstraction allocation that suit for above requirements.
Storage In Sensor Network(Cont.)
Flash memory semantics Some part (called erase sectors) must
be erased before overwriting.
Flash memory: 1.NOR flash (good for read)
2.NAND flash (good for storage)
COFFEE
Coffee is a portable, high-speed file system for sensor device equipped with flash memories.
Micro logs to handle file modifications.
Use a small footprint: each open file O(1) RAM.
COFFEE (Cont.)
Design principles Memory and code size constraints. Small memory footprints-regardless
of the file sizes. Rule:
1.divided into erase sectors of size 2.Erease sets all bits to 1 3.Programming switches a subset of the
bits in a page from 1 to 0.
COFFEE (Cont.)
COFFEE (Cont.)
Page Structure
A file is stored as a contiguous group Page Allocation Algorithm: first-fit policy.
Minimizing metadata in the RAM (metadata in first page of file)
Locating File File cache for locations. If not in cache => cache miss(sequentially scan)
Garbage Collection
Wear Leveling Policy What is wear leveling Erase too much -> memory corrupt Method: delay garbage collection until a
space reservation request cannot be fulfilled.
Evaluation
Conclusion
Coffee’s high throughput and low latency make it a suitable underlying layer for storage abstractions.