DOCSLIB.ORG

Study of File System Evolution

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Study of File System Evolution Study of File System Evolution Swaminathan Sundararaman, Sriram Subramanian Department of Computer Science University of Wisconsin {swami, srirams} @cs.wisc.edu Abstract File systems have traditionally been a major area of file systems are typically developed and maintained by research and development. This is evident from the several programmer across the globe. At any point in existence of over 50 file systems of varying popularity time, for a file system, there are three to six active in the current version of the Linux kernel. They developers, ten to fifteen patch contributors but a single represent a complex subsystem of the kernel, with each maintainer. These people communicate through file system employing different strategies for tackling individual file system mailing lists [14, 16, 18] various issues. Although there are many file systems in submitting proposals for new features, enhancements, Linux, there has been no prior work (to the best of our reporting bugs, submitting and reviewing patches for knowledge) on understanding how file systems evolve. known bugs. The problems with the open source We believe that such information would be useful to the development approach is that all communication is file system community allowing developers to learn buried in the mailing list archives and aren’t easily from previous experiences. accessible to others. As a result when new file systems are developed they do not leverage past experience and This paper looks at six file systems (Ext2, Ext3, Ext4, could end up re-inventing the wheel. To make things JFS, ReiserFS, and XFS) from a historical perspective worse, people could typically end up doing the same (between kernel versions 1.0 to 2.6) to get an insight on mistakes as done in other file systems. the file system development process. We study the source code of these file systems over years to observe We chose to look at the file systems in the Linux kernel changes in complexity of the system and relate these for the following three reasons: (1) Linux is open metrics to the features and stability of file systems. We source, implying that we can get access to the source identified that only a few components in file systems code of the file systems, without which it is almost are difficult to get right the first time. Also, file impossible to study their evolution. (2) As compared to system developers do not learn from each others other systems Linux support a large variety of file mistake. As a result they end up introducing the same systems. Most importantly, some of these have existed bugs in file systems. for a long time (10-15 years). Hence, it is possible to look at the file systems during different stages of its 1. Introduction lifetime and derive conclusions from them. (3) All communications (discussion, patches, bugs, etc.) In today’s world everything revolves around data. Data between file system developers can be obtained from is critical for day-to-day operation of any system. Data the mailing list and are publicly available in many management is taken care of by file systems which websites [16]. The bugzilla database, CVS, and git reliably store data on disks. Users typically have varied repositories are also publicly accessible. This allowed requirements ranging from scalability, availability, us to get insight into the development process of file fault-tolerance, performance guarantees in business systems in an open source environment. It would environment to small memory footprints, security, definitely be interesting to look at file systems in other reliability in desktop environments. This has driven the operating systems like Solaris, BSD. or Windows to file system community to develop a variety of systems compare and contrast it with file systems developed in that cater to different user requirements. Linux. An open source environment like Linux has around 50 In this paper, we look at file system code in the Linux different file systems that provide different guarantees, kernel (version numbers 1.0 to 2.6). This covers 14 targeting varied media. In an open source environment, years of kernel development (1994 to 2008). We also look at patches, bug reports and other communication that is available in each of the file system mailing list. frequently changed components. Section 7 discusses We have built a tool that automatically crawls the common bugs in file systems code and looks at turn mailing archives and extracts higher level information around time for bugs in XFS. We talk about the from them. We did not use Bugzilla database [9] as it is implications of this work and how open source restricted to Redhat releases and they are only a subset community should adapt itself for more efficient of the changes that are available in the mailing lists. We functioning in Section 8. We comment on related work did not use the CVS repositories for the file systems as in Section 9 and conclude in Section 10. they didn't have complete information. The repositories are solely used by the file system maintainer to 2. Problems in the Open Source Model consolidate the patches that developers submit over time and eventually the kernel maintainer picks up the To our knowledge, there has been no prior work on patches from each of the maintainers and integrates it to understanding the file system development process, the linux kernel. We already have this information by especially in the Linux world. Previous work on looking at the file system code between kernel releases software evolution looked at software repositories like and the mailing list. As far as we know, a study of CVS, etc[3,4]. We cannot apply the same kind of similar nature does not exist in the file system analysis because the development model in Linux is community. very different. There is to no easy way to get this information in the Linux world. We comment briefly The contributions of this paper are as follows: about the file system development process in Linux to understand the difficulties involved in it. • We have developed tools to systematically mine information available in mailing lists [14,15,16,18] and source code repositories [10, 11] so that developers can easily query to know file system properties or bugs. • As part of our preliminary analysis, we provide insights into the development process, common problem areas, and stability of file systems. • Identification of common bugs in file systems. This could serve as a reference document to file system developers to check if their file system are immune to the common bugs. From our study, we found that out of 60 or so file systems only a handful of them have lots of features and most widely developed and used. Most of the file systems are designed well and do not undergo design level changes during their lifetime. In a purely open source file system, many developers do contribute to the development of the file system and in contrast file systems that have been started. We also found that developers across file system do not communicate Figure 1: Linux kernel development process effectively and as a result end up repeating the same mistakes in their file systems. Figure 1 shows the development process in linux. From Rest of the paper is organized as follows. Sections 2 the figure, one can see that most of the communication explains the difficulties in extracting higher level between the developers happens through the mailing information in file system development in Linux. lists. All the discussion, patches, and issues get buried Section 3 gives a broad overview of file system in the in the mails and finally end up getting archived at some latest Linux kernel and justifies our choice of file public website (e.g., [16]). Unlike the software systems included in this study. Section 4 analyzes the development process employed in other open source trends in code change and complexity across file projects, the Linux model is very different in the sense systems. Section 5 and Section 6 looks at the code that there is no proper CVS repository where we can contributions of developers in file systems and track every change in the file system. Everything has to Figure 2. Lines of Code for all file systems in Linux 2.6.27 be inferred from the mails in the mailing lists. Although study. The Ext2 file system was chosen because it is a there are search engines that help extract information mature file system that was derived from the Ext file quickly from these archives, there are not tools that can system and has been around for more than 15 years. infer trends and features from these mails. To our Also, Ext2 was the default file system for Linux for knowledge, existing tools to understand the open source over 10 years which indicates its stability. We chose the project [7] etc. do not work well for extracting Ext3 and Ext4 because they were derived from Ext2. information from the file systems in Linux. To Ext3 is a mature file system (it is now the default file summarize, file system developers typically system in Linux) and the development in Ext4 started communicate within their community (file system recently (in 1995). The Ext2/3/4 file system were mailing list) about the issues and fixes and there is no started by the open source community. ReiserFS was easy way to get this information to other file system chosen as it was initially conceived by a single person developers. As a result, we believe that file system (Hans Reiser) and was slowly adopted by the open developers do not learn from each other’s mistakes and source community.
Load more

Recommended publications
  • Membrane: Operating System Support for Restartable File Systems Swaminathan Sundararaman, Sriram Subramanian, Abhishek Rajimwale, Andrea C
    Membrane: Operating System Support for Restartable File Systems Swaminathan Sundararaman, Sriram Subramanian, Abhishek Rajimwale, Andrea C. Arpaci-Dusseau, Remzi H. Arpaci-Dusseau, Michael M. Swift Computer Sciences Department, University of Wisconsin, Madison Abstract and most complex code bases in the kernel. Further, We introduce Membrane, a set of changes to the oper- file systems are still under active development, and new ating system to support restartable file systems. Mem- ones are introduced quite frequently. For example, Linux brane allows an operating system to tolerate a broad has many established file systems, including ext2 [34], class of file system failures and does so while remain- ext3 [35], reiserfs [27], and still there is great interest in ing transparent to running applications; upon failure, the next-generation file systems such as Linux ext4 and btrfs. file system restarts, its state is restored, and pending ap- Thus, file systems are large, complex, and under develop- plication requests are serviced as if no failure had oc- ment, the perfect storm for numerous bugs to arise. curred. Membrane provides transparent recovery through Because of the likely presence of flaws in their imple- a lightweight logging and checkpoint infrastructure, and mentation, it is critical to consider how to recover from includes novel techniques to improve performance and file system crashes as well. Unfortunately, we cannot di- correctness of its fault-anticipation and recovery machin- rectly apply previous work from the device-driver litera- ery. We tested Membrane with ext2, ext3, and VFAT. ture to improving file-system fault recovery. File systems, Through experimentation, we show that Membrane in- unlike device drivers, are extremely stateful, as they man- duces little performance overhead and can tolerate a wide age vast amounts of both in-memory and persistent data; range of file system crashes.
    [Show full text]
  • ECE 598 – Advanced Operating Systems Lecture 19
    ECE 598 { Advanced Operating Systems Lecture 19 Vince Weaver http://web.eece.maine.edu/~vweaver [email protected] 7 April 2016 Announcements • Homework #7 was due • Homework #8 will be posted 1 Why use FAT over ext2? • FAT simpler, easy to code • FAT supported on all major OSes • ext2 faster, more robust filename and permissions 2 btrfs • B-tree fs (similar to a binary tree, but with pages full of leaves) • overwrite filesystem (overwite on modify) vs CoW • Copy on write. When write to a file, old data not overwritten. Since old data not over-written, crash recovery better Eventually old data garbage collected • Data in extents 3 • Copy-on-write • Forest of trees: { sub-volumes { extent-allocation { checksum tree { chunk device { reloc • On-line defragmentation • On-line volume growth 4 • Built-in RAID • Transparent compression • Snapshots • Checksums on data and meta-data • De-duplication • Cloning { can make an exact snapshot of file, copy-on- write different than link, different inodles but same blocks 5 Embedded • Designed to be small, simple, read-only? • romfs { 32 byte header (magic, size, checksum,name) { Repeating files (pointer to next [0 if none]), info, size, checksum, file name, file data • cramfs 6 ZFS Advanced OS from Sun/Oracle. Similar in idea to btrfs indirect still, not extent based? 7 ReFS Resilient FS, Microsoft's answer to brtfs and zfs 8 Networked File Systems • Allow a centralized file server to export a filesystem to multiple clients. • Provide file level access, not just raw blocks (NBD) • Clustered filesystems also exist, where multiple servers work in conjunction.
    [Show full text]
  • Ext4 File System and Crash Consistency
    1 Ext4 file system and crash consistency Changwoo Min 2 Summary of last lectures • Tools: building, exploring, and debugging Linux kernel • Core kernel infrastructure • Process management & scheduling • Interrupt & interrupt handler • Kernel synchronization • Memory management • Virtual file system • Page cache and page fault 3 Today: ext4 file system and crash consistency • File system in Linux kernel • Design considerations of a file system • History of file system • On-disk structure of Ext4 • File operations • Crash consistency 4 File system in Linux kernel User space application (ex: cp) User-space Syscalls: open, read, write, etc. Kernel-space VFS: Virtual File System Filesystems ext4 FAT32 JFFS2 Block layer Hardware Embedded Hard disk USB drive flash 5 What is a file system fundamentally? int main(int argc, char *argv[]) { int fd; char buffer[4096]; struct stat_buf; DIR *dir; struct dirent *entry; /* 1. Path name -> inode mapping */ fd = open("/home/lkp/hello.c" , O_RDONLY); /* 2. File offset -> disk block address mapping */ pread(fd, buffer, sizeof(buffer), 0); /* 3. File meta data operation */ fstat(fd, &stat_buf); printf("file size = %d\n", stat_buf.st_size); /* 4. Directory operation */ dir = opendir("/home"); entry = readdir(dir); printf("dir = %s\n", entry->d_name); return 0; } 6 Why do we care EXT4 file system? • Most widely-deployed file system • Default file system of major Linux distributions • File system used in Google data center • Default file system of Android kernel • Follows the traditional file system design 7 History of file system design 8 UFS (Unix File System) • The original UNIX file system • Design by Dennis Ritche and Ken Thompson (1974) • The first Linux file system (ext) and Minix FS has a similar layout 9 UFS (Unix File System) • Performance problem of UFS (and the first Linux file system) • Especially, long seek time between an inode and data block 10 FFS (Fast File System) • The file system of BSD UNIX • Designed by Marshall Kirk McKusick, et al.
    [Show full text]
  • W4118: Linux File Systems
    W4118: Linux file systems Instructor: Junfeng Yang References: Modern Operating Systems (3rd edition), Operating Systems Concepts (8th edition), previous W4118, and OS at MIT, Stanford, and UWisc File systems in Linux Linux Second Extended File System (Ext2) . What is the EXT2 on-disk layout? . What is the EXT2 directory structure? Linux Third Extended File System (Ext3) . What is the file system consistency problem? . How to solve the consistency problem using journaling? Virtual File System (VFS) . What is VFS? . What are the key data structures of Linux VFS? 1 Ext2 “Standard” Linux File System . Was the most commonly used before ext3 came out Uses FFS like layout . Each FS is composed of identical block groups . Allocation is designed to improve locality inodes contain pointers (32 bits) to blocks . Direct, Indirect, Double Indirect, Triple Indirect . Maximum file size: 4.1TB (4K Blocks) . Maximum file system size: 16TB (4K Blocks) On-disk structures defined in include/linux/ext2_fs.h 2 Ext2 Disk Layout Files in the same directory are stored in the same block group Files in different directories are spread among the block groups Picture from Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 3 Block Addressing in Ext2 Twelve “direct” blocks Data Data BlockData Inode Block Block BLKSIZE/4 Indirect Data Data Blocks BlockData Block Data (BLKSIZE/4)2 Indirect Block Data BlockData Blocks Block Double Block Indirect Indirect Blocks Data Data Data (BLKSIZE/4)3 BlockData Data Indirect Block BlockData Block Block Triple Double Blocks Block Indirect Indirect Data Indirect Data BlockData Blocks Block Block Picture from Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc.
    [Show full text]
  • Solid State Copier DP-250-BD-XL Or DVD
    ® SOLE SOURCE PROVIDER OF EVIDENCE GRADE PRODUCTS EVIDENCE - SURVEILLANCE - DIGITAL & ANALOG RECORDING PRODUCTS & EQUIPMENT Solid State Copier DP-250-BD-XL or DVD Flash to Flash, Flash to Optical and Optical to Flash Media copier designed for secure, high speed transfer of data without requiring a computer or network connectivity. Ruggedized design for both desktop and portable use. ✓ Perfect for copying Original Evidence - Stand Alone operation, No computer or network connection available or required. .No Edit functions ✓ Secure Transfer, perfect for data, pictures, video and audio ✓ High Speed Capability (16x BD/24x DVD/48x CD) ✓ Ruggedized Aluminum Case designed for Desktop and Portable operation. ✓ Two Models available: ✓ DP-250-DVD (DVD/CD) ✓ DP-250-BD-XL (Blu-Ray, BD-XL/DVD/CD) Key Features (DP-250) Stand Alone operation, no computer required, LCD display of current function selected. Secure Transfer o No Hard Drive or Memory retention of the copied or original data when powered off. o No edit functions, No connectivity to a Network or external computer. o Original date and time transferred to the copy. Supports most open format USB Devices. Supports all types of Flash Cards formatted in FAT16, FAT32, exFAT, ext2, ext3, ext4, HFS, HFS+. Burn Speed Settable. (16X BD/24X DVD/48X CD) Supports Flash to Flash, Flash to Disc and Disc to Flash Copying. Allows data appending to a USB/Flash device without erasing the existing data content. Supports Selective file copying, Multi-Session and Disc Spanning. (Flash to Optical) Copy, Copy & Compare, Copy Select & Multi-Session. (Flash to Optical) Rugged Aluminum case for Desktop and Portable use.
    [Show full text]
  • Hardware-Driven Evolution in Storage Software by Zev Weiss A
    Hardware-Driven Evolution in Storage Software by Zev Weiss A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Computer Sciences) at the UNIVERSITY OF WISCONSIN–MADISON 2018 Date of final oral examination: June 8, 2018 ii The dissertation is approved by the following members of the Final Oral Committee: Andrea C. Arpaci-Dusseau, Professor, Computer Sciences Remzi H. Arpaci-Dusseau, Professor, Computer Sciences Michael M. Swift, Professor, Computer Sciences Karthikeyan Sankaralingam, Professor, Computer Sciences Johannes Wallmann, Associate Professor, Mead Witter School of Music i © Copyright by Zev Weiss 2018 All Rights Reserved ii To my parents, for their endless support, and my cousin Charlie, one of the kindest people I’ve ever known. iii Acknowledgments I have taken what might be politely called a “scenic route” of sorts through grad school. While Ph.D. students more focused on a rapid graduation turnaround time might find this regrettable, I am glad to have done so, in part because it has afforded me the opportunities to meet and work with so many excellent people along the way. I owe debts of gratitude to a large cast of characters: To my advisors, Andrea and Remzi Arpaci-Dusseau. It is one of the most common pieces of wisdom imparted on incoming grad students that one’s relationship with one’s advisor (or advisors) is perhaps the single most important factor in whether these years of your life will be pleasant or unpleasant, and I feel exceptionally fortunate to have ended up iv with the advisors that I’ve had.
    [Show full text]
  • The Linux Device File-System
    The Linux Device File-System Richard Gooch EMC Corporation [email protected] Abstract 1 Introduction All Unix systems provide access to hardware via de- vice drivers. These drivers need to provide entry points for user-space applications and system tools to access the hardware. Following the \everything is a file” philosophy of Unix, these entry points are ex- posed in the file name-space, and are called \device The Device File-System (devfs) provides a power- special files” or \device nodes". ful new device management mechanism for Linux. Unlike other existing and proposed device manage- This paper discusses how these device nodes are cre- ment schemes, it is powerful, flexible, scalable and ated and managed in conventional Unix systems and efficient. the limitations this scheme imposes. An alternative mechanism is then presented. It is an alternative to conventional disc-based char- acter and block special devices. Kernel device drivers can register devices by name rather than de- vice numbers, and these device entries will appear in the file-system automatically. 1.1 Device numbers Devfs provides an immediate benefit to system ad- ministrators, as it implements a device naming scheme which is more convenient for large systems Conventional Unix systems have the concept of a (providing a topology-based name-space) and small \device number". Each instance of a driver and systems (via a device-class based name-space) alike. hardware component is assigned a unique device number. Within the kernel, this device number is Device driver authors can benefit from devfs by used to refer to the hardware and driver instance.
    [Show full text]
  • Filesystem Considerations for Embedded Devices ELC2015 03/25/15
    Filesystem considerations for embedded devices ELC2015 03/25/15 Tristan Lelong Senior embedded software engineer Filesystem considerations ABSTRACT The goal of this presentation is to answer a question asked by several customers: which filesystem should you use within your embedded design’s eMMC/SDCard? These storage devices use a standard block interface, compatible with traditional filesystems, but constraints are not those of desktop PC environments. EXT2/3/4, BTRFS, F2FS are the first of many solutions which come to mind, but how do they all compare? Typical queries include performance, longevity, tools availability, support, and power loss robustness. This presentation will not dive into implementation details but will instead summarize provided answers with the help of various figures and meaningful test results. 2 TABLE OF CONTENTS 1. Introduction 2. Block devices 3. Available filesystems 4. Performances 5. Tools 6. Reliability 7. Conclusion Filesystem considerations ABOUT THE AUTHOR • Tristan Lelong • Embedded software engineer @ Adeneo Embedded • French, living in the Pacific northwest • Embedded software, free software, and Linux kernel enthusiast. 4 Introduction Filesystem considerations Introduction INTRODUCTION More and more embedded designs rely on smart memory chips rather than bare NAND or NOR. This presentation will start by describing: • Some context to help understand the differences between NAND and MMC • Some typical requirements found in embedded devices designs • Potential filesystems to use on MMC devices 6 Filesystem considerations Introduction INTRODUCTION Focus will then move to block filesystems. How they are supported, what feature do they advertise. To help understand how they compare, we will present some benchmarks and comparisons regarding: • Tools • Reliability • Performances 7 Block devices Filesystem considerations Block devices MMC, EMMC, SD CARD Vocabulary: • MMC: MultiMediaCard is a memory card unveiled in 1997 by SanDisk and Siemens based on NAND flash memory.
    [Show full text]
  • Enterprise Filesystems
    Enterprise Filesystems Eric Sandeen Principal Software Engineer, Red Hat Feb 21, 2013 1 ERIC SANDEEN What We'll Cover ● Local “Enterprise-ready” Linux filesystems ● Ext3 ● Ext4 ● XFS ● BTRFS ● Use cases, features, pros & cons of each ● Recent & future work ● Features ● Scalability ● Benchmarks 2 ERIC SANDEEN Local Filesystems in RHEL6 ● We ship what customers need and can rely on ● We ship what we test and support ● Major on-disk local filesystems ● Ext3, Ext4, XFS, BTRFS* ● Others are available for special purposes ● fat, vfat, msdos, udf, cramfs, squashfs... ● We'll cover the “big four” today 3 ERIC SANDEEN The Ext3 filesystem ● Ext3 is was the most common file system in Linux ● Most distributions historically used it as their default ● Applications tuned to its specific behaviors (fsync...) ● Familiar to most system administrators ● Ext3 challenges ● File system repair (fsck) time can be extremely long ● Limited scalability - maximum file system size of 16TB ● Can be significantly slower than other local file systems ● direct/indirect, bitmaps, no delalloc ... 4 ERIC SANDEEN The Ext4 filesystem ● Ext4 has many compelling new features ● Extent based allocation ● Faster fsck time (up to 10x over ext3) ● Delayed allocation, preallocation ● Higher bandwidth ● Should be relatively familiar for existing ext3 users ● Ext4 challenges ● Large device support not polished in its user space tools ● Limits supported maximum file system size to 16TB* ● Has different behavior over system failure 5 ERIC SANDEEN The XFS filesystem ● XFS is very robust
    [Show full text]
  • Zack's Kernel News
    KERNEL NEWS ZACK’S KERNEL NEWS ReiserFS Turmoil Their longer term plan, Alexander Multiport Card driver, again naming In light of recent events surrounding says, depends on what happens with himself the maintainer. Hans Reiser (http:// www. linux-maga- Hans. If Hans is released, the developers Jiri’s been submitting a number of zine. com/ issue/ 73/ Linux_World_News. intend to proceed as before. If he is not patches for these drivers, so it makes pdf), the question of how to continue released, Alexander’s best guess is that sense he would maintain them if he ReiserFS development came up on the the developers will try to appoint a wished; in any event, no other kernel linux-kernel mailing list. Alexander proxy to run Namesys. hacker has spoken up to claim the role. Lyamin from Hans’s Namesys company offered his take on the situation. He said Status of sysctl Filesystem Benchmarks that ReiserFS 3 has pretty much stabi- In keeping with Linus Torvalds’ recent Some early tests have indicated that ext4 lized into bugfix mode, though Suse assertions that it is never acceptable to is faster with disk writes than either ext3 folks had been adding new features like break user-space, Albert Cahalan volun- or Reiser4. There was general interest in ACL support. So ReiserFS 3 would go on teered to maintain the sysctl code if it these results, though the tests had some as before. couldn’t be removed. But Linus pointed problems (the tester thought delayed In terms of Reiser4, however, Alexan- out that really nothing actually used allocation was part of ext4, when that der said that he and the other Reiser de- sysctl (the implication being that it feature has not yet been merged into velopers were still addressing the techni- wouldn’t actually break anything to get Andrew Morton’s tree).
    [Show full text]
  • CIS Ubuntu Linux 18.04 LTS Benchmark
    CIS Ubuntu Linux 18.04 LTS Benchmark v1.0.0 - 08-13-2018 Terms of Use Please see the below link for our current terms of use: https://www.cisecurity.org/cis-securesuite/cis-securesuite-membership-terms-of-use/ 1 | P a g e Table of Contents Terms of Use ........................................................................................................................................................... 1 Overview ............................................................................................................................................................... 12 Intended Audience ........................................................................................................................................ 12 Consensus Guidance ..................................................................................................................................... 13 Typographical Conventions ...................................................................................................................... 14 Scoring Information ..................................................................................................................................... 14 Profile Definitions ......................................................................................................................................... 15 Acknowledgements ...................................................................................................................................... 17 Recommendations ............................................................................................................................................
    [Show full text]
  • Model-Based Failure Analysis of Journaling File Systems
    Model-Based Failure Analysis of Journaling File Systems Vijayan Prabhakaran, Andrea C. Arpaci-Dusseau, and Remzi H. Arpaci-Dusseau University of Wisconsin, Madison Computer Sciences Department 1210, West Dayton Street, Madison, Wisconsin {vijayan, dusseau, remzi}@cs.wisc.edu Abstract To analyze such file systems, we develop a novel model- based fault-injection technique. Specifically, for the file We propose a novel method to measure the dependability system under test, we develop an abstract model of its up- of journaling file systems. In our approach, we build models date behavior, e.g., how it orders writes to disk to maintain of how journaling file systems must behave under different file system consistency. By using such a model, we can journaling modes and use these models to analyze file sys- inject faults at various “interesting” points during a file sys- tem behavior under disk failures. Using our techniques, we tem transaction, and thus monitor how the system reacts to measure the robustness of three important Linux journaling such failures. In this paper, we focus only on write failures file systems: ext3, Reiserfs and IBM JFS. From our anal- because file system writes are those that change the on-disk ysis, we identify several design flaws and correctness bugs state and can potentially lead to corruption if not properly present in these file systems, which can cause serious file handled. system errors ranging from data corruption to unmountable We use this fault-injection methodology to test three file systems. widely used Linux journaling file systems: ext3 [19], Reis- erfs [14] and IBM JFS [1].
    [Show full text]