The Conquest File System: An-I A. Wang Geoffrey H. Kuenning Peter Reiher Gerald J. Popek Life after Disks 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 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. Motivation Conquest Architecture Conquest Benefits Problems: Modern file systems are designed for disks  Disk becoming increasingly worse system bottleneck  Growing complexity 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? 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. 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 the LRU disk cache Year $/MB (log) paper/film 3.5” HDD 2.5” HDD 1” HDD persistent RAM Booming of digital photography 4 to 10 GB of persistent RAM on high-end machines Conquest File System Simplified IO buffer management IO buffer Storage requests Simplified disk management Disk Simplified persistence support Battery-backed RAM 10% 90% File system boundary Small file and metadata storage Large-file-only file system ATA/SCSI/IDE Conventional file systems IO buffer Disk management Storage requests IO buffer management Disk File system boundary ATA/SCSI/IDE Persistence support 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 Conventional Data Path IO buffer Disk management Storage requests IO buffer management Disk Persistence support Simplified metadata allocation Memory manager encapsulation Simplified persistence support Battery-backed RAM Small file and metadata storage Conquest Memory Data Path Storage requests Buffer allocation management Buffer garbage collection Data caching Simplified predictive readahead Simplified write behind Simplified cache replacement Simplified disk layout Simplified disk management Conquest Disk Data Path Simplified IO buffer management IO buffer Storage requests Disk Small file and metadata storage Large-file-only file system Battery-backed RAM 2 GB physical RAM > RAM<= RAM