The Conquest File System:

1. Booming of digital photography 102 4 to 10 GB of persistent RAM on high-end machines 101 100 $/MB (log) paper/film persistent RAM 10-1 1” HDD 2.5” HDD 10-2 3.5” HDD 1995 2000 2005 Year Conventionalfile systems Storage requests IO buffer management IO buffer Persistence support Disk management Conquest File System ATA/SCSI/IDE Storage requests 10% 90% Disk Simplified persistence support Simplified IO buffer management Battery-backed RAM File system boundary IO buffer Small file and metadata storage Simplified disk management ATA/SCSI/IDE Disk Large-file-only file system File system boundary ConventionalData Path Conquest Disk Data Path Conquest Memory Data Path Storage requests Storage requests Storage requests IO buffer management Simplified IO buffer management Buffer allocation management Buffer garbage collection Data caching Metadata caching Predictive readahead Write behind Cache replacement Metadata allocation Metadata placement Metadata translation Disk layout Fragmentation management Simplified persistence support IO buffer Buffer allocation management Buffer garbage collection Data caching Simplified predictive readahead Simplified write behind Simplified cache replacement Simplified disk layout Battery-backed RAM IO buffer Battery-backed RAM Small file and metadata storage Persistence support Small file and metadata storage Simplified disk management Disk management Simplified metadata allocation Memory manager encapsulation Disk Disk Large-file-only file system 2 GB physical RAM <= RAM > RAM The Conquest File System: Life after Disks An-I A. Wang • Geoffrey H. Kuenning • Peter Reiher • Gerald J. Popek Motivation Problems: Modern file systems are designed for disks Disk becoming increasingly worse system bottleneck Growingcomplexity to mask the disk performance Observation:Cost of persistent RAM (e.g., battery-backed DRAM) is rapidly declining Question: How do we design a file system that exploits the abundance of RAM? Abstract The rapidly declining cost of persistent RAM technologies prompts the question of when, not whether, such memory will become the preferred storage medium for many computers. Conquest is a file system that provides a transition from disk to persistent RAM as the primary storage medium. Conquest Conquest Architecture Conquest provides two specialized and simplified data paths to in-core and on-disk storage, and Conquest realizes most of the benefits of persistent RAM at a fractional cost of a RAM-only solution. As of October 2001, Conquest can be used effectively for a hardware cost of under $200. We compare Conquest’s performance to ext2, reiserfs, SGI XFS, and ramfs, using popular benchmarks. Our measurements show that Conquest incurs little overhead compared to ramfs. Compared to the disk-based file systems, Conquest achieves 24% to 1900% faster memory performance, and 43% to 96% faster performance when exercising both memory and disk. Conquest uses memory to store all metadata (file attributes), small files, executables, and shared libraries, leaving only the content of large files on disk. All accesses to in-core data and metadata incur no data duplication or disk-related overhead, and executions are in-place. Because most accesses to large files are sequential, we can relax many historical disk design constraints. Conquest Benefits Persistence: Conquest memory storage survives reboots Capacity:Conquest is not limited by the physical size of the memory Simplicity: Conquest consists of two simplified data paths, with at least 20% fewer semicolons compared to ext2, reiserfs, and SGI XFS) Performance:Conquest is at least 24% faster than ext2, reiserfs, and SGI XFS, operating under theLRU disk cache