File system concepts

Transcription

1 File system concepts

2 Ease of searching a specific data File to group data: variable size, naming Directory to group files File system concepts File name, file offset Directory File name, file offset File data File data

3 Unix file systems history 1970 Unix file system (System V, 1974) 1980 Berkeley fast file system (BSD 4.2, 1984) Minix file system (Minix, 1987) 1990 HFS (1985) Extended file system (Linux, 1992) Ext2 file system (1993) Journaling file system (AIX, 1990) Journaling file system (OS/2, 1999) HFS+ (1998) XFS (IRIX, 1994) Log-structured file system (1991) 2000 Ext3 file system (2001) Ext4 file system (2008) 2010 Journaling file system (Linux, 2001) BTRFS (2009) XFS (Linux, 2002) F2FS (2012)

4 DOS/Windows file systems history File Allocation Table FAT (8bit, 1977) / FAT12 (1980) / FAT16 (1984) Target for floppy disk HPFS (OS/2, 1989) FAT32/VFAT (1996) exfat (2006) NTFS Since Windows NT 3.1 (1993)

5 Network/distributed file systems Network file systems Mount remote file system to local directory Network File System Server Message Block/CiFS (samba) AppleTalk Filing Protocol Distributed file systems Share storage device to build a large file system Andrew File System Google file system Hadoop file system (HDFS)

6 File system interfaces R. C. Daley, P. G. Neumann, A General-Purpose File System For Secondary Storage, 1965 Defined what a file system is and how it works Concepts of user, file, directory, directory hierarchy Backup storage and their usage Incremental backup / weekly full backup recovery POSIX [IEEE 1003 / Richard Stallman / 1988] Standardized file system interfaces Standard I/O API Direct I/O API Memory mapped I/O API

7 File system interface : stream I/O Buffered and line-by-line I/O interface Header: <stdio.h> Handler: FILE *f; Functions fopen, fclose fprintf, fscanf fgets, fputs fread, fwrite fseek, ftell #include <stdio.h> int main(void) { FILE *fp; char *str; if ( fp = fopen("main.c", "r") ) { str = malloc(4096); } while( fgets(str, 4095, fp) ) printf("%s", str); fclose(fp); free(str); } return 0;

8 File system interface : direct I/O Header: <fcntl.h>, <unistd.h>, Handler: int fd; Functions open, creat, close read, write lseek, lseek64 posix_fallocate, posix_fadvise #include <fcntl.h> #include <unistd.h> int main(void) { int fd; void *buf; if ( (fd = open("main.c", "r")) > 0) { buf = malloc(4096); } while( read(fd, buf, 4096) > 0) write(1, buf, 4096); close(fd); free(buf); } return 0;

9 File system interface : mmap I/O Memory access to read/write a file Header: <sys/mman.h> Handler: void *ptr; Functions void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset) int munmap(void *addr, size_t length)

10 Example File system interface : mmap I/O #include <fcntl.h> #include <unistd.h> #include <sys/mman.h> int main(void) { int fd, length; void *buf; if ( (fd = open("main.c", "r")) > 0) { length = lseek(fd, 0, SEEK_END); buf = mmap(null, length, PROT_READ, MAP_PRIVATE, fd, 0); write(1, buf, length); munmap(buf, length); close(fd); } } return 0;

11 Stream I/O illustrated fopen fgets Hello, fgets Application fprintf World fflush fclose Hello, Guys libc Hello, World open read write close sys_open sys_read VFS sys_write sys_close Page cache Hello, Guys

12 Memory mapped I/O illustrated Application mmap c=buf[0] buf[1]= \n munmap libc sys_mmap VFS sys_munmap pagefault aops->readpage() Page cache 동해물과백두산이마르고닳도록하느님이보우하사우리나라만세무궁화삼천리화려강산 aops->writepage() replacement 동해물과백두산이마르고닳도록하느님이보우하사우리나라만세무궁화삼천리화려강산

13 File system benchmarks IOzone Iometer Filebench FFSB sysbench Bonnie Postmark TPC SPECsfs dbench 65

14 IOzone File I/O performance analysis Installation apt-get install iozone3 Parameters -s filesize_kb -r record_size_kb -f [path]filename -i test -a / -A / -z / -Z : auto mode -t children -i Description 0 write/rewrite 1 read/re-read 2 random-read/write 3 read-backwards 4 re-write-record 5 stride-read 6 fwrite/re-fwrite 7 fread/re-fread 8 random_mix 9 pwrite/re-pwrite 10 pread/re-pread 11 pwritev/re-pwritev 12 preadv/re-preadv 66

15 Filebench File system operation analysis Installation oad configure ; make; make install workloads 67 Execution go_filebench load workload ( /share/filebench/workloads/*) set $dir=path run duration quit filemicro_... singlestream... fivestream... random... fileserver networkfs oltp varmail webserver videoserer

16 Postmark Mail-server workload simulation Installation apt-get install postmark Distributed as a C source file Execution postmark config Commands set size set number set transactions set location run quit 68

17 A modular, cross-platform and multi-threaded benchmark tool Target: CPU, memory, threads, mutex, fileio, oltp Installation apt-get install sysbench Parameters --test=fileio --file-test-mode=rndwr --file-total-size=1g --file-block-size=16k command: prepare, run, cleanup Sysbench

18 File system design

19 Space allocation File system design elements Contiguous allocation vs. fragmented allocation File to block mapping management Managing free space Name space management File naming: name length, case sensitivity, ex. early UNIX file system / FAT uses 8.3 naming system Directory hierarchy Single level array Tree-structured multi-level directory graph-structured directory

20 Disk layout and file abstraction Superblock Dir b Inode a File a, 0 File a, 1? Abstractions in file system File data Inode: per file metadata name, size, data location, modified time, owner, Directory hierarchy Superblock Meta data for free space management

21 Allocated/free space management Bitmap approach (ext*fs) Low storage capacity usage High free space search cost Linked List approach (FAT) Low free space search cost

22 Allocated/free space management Tree-based approach Inode and indirect blocks inode filename attributes direct blocks single indirect double indirect triple indirect Indirect block Indirect block Indirect block Indirect block Extents: (start block number, contiguous blocks) data data data data data data data data data data

23 Allocated/free space management Tree-based approach B-Tree (XFS, btrfs, ) Useful for extent-based allocation File allocation 4 Free space (1, 3) (7, 1) (10, 4) (14, 5) (4, 3) (8, 2) (0, 1)

24 Directory implementation Array Easy to manage File name length limit RUN.EXE README.TXT DATA.DB Linear list Variable length file name Hard to manage RUN.EXE README.TXT DATA.DB Long named file.docx Hash table Indexed by file name: fast search Hash collision

25 Example: FAT

26 Characteristics Background: 1970s Personal computer Floppy disks (~ 1MB) 8.3 name space Case insensitive Long name format extension No protection mechanism No consistency guarantee chkdsk, diskscan

27 File data location management Linked list approach File allocation table FAT Root dir. Data Boot block Backup A.EXE FAT entry (1 entry / 1 cluster) Next cluster number (cluster: 512 bytes ~ 32 KB) 0: free, -1: end of file

28 A special file with 32 bytes directory entries Directory Entries File name: 11 bytes (name 8, extension 3) Attributes Read-only, hidden, system, sub-directory, archive, long file name ctime, atime, mtime Year (7), month (4), day (5), hour (5), min (6), second/2 (5) First data cluster File size (max. 4 GB)

29 Long name extension Combining consecutive directory entries First entry: normal directory entry (first 11 character) LFN entries File name segment: 26 bytes Reserved critical entries First data cluster File type, sequence number, etc. Introductio 0 ctime atime mtime FDC length L n to File F System.pptx 0 Sequence File type First cluster, for compatibility

30 Boot sector Boot strap File system summary File system size (sectors) Logical sector size Cluster size # of FATs Root directory entries Root directory first cluster Volume label Drive number

31 Next free cluster pointer Free space management FAT32 maintains last allocated cluster number Possible to undelete recently delete files Produces fragmentation Last allocated cluster

32 Example: ext3

33 Background Characteristics Linux operating system: multi-user Evolving for from desktop to server and real-time system Based on block groups Each block group works as an independent file system Inode, directory, file data Inodes for allocation and attribute management Journaling support from ext3

34 Ext file system = an array of block groups Block group bg_block_bitmap, bg_inode_bitmap, bg_inode_table bg_free_blocks_count, bg_free_inodes_count, Block group size: determined by block size 4K block 128MB Why? Data block bitmap must fit in a block

35 Size: 128-byte / 256-byte (ext4) Inode

36 Directory ext3~ supports HTree: hashing for entry lookup [Daniel Phillips, A Directory Index for Ext2, Linux Symposium 02]

37 Free space management Data block bitmap / inode bitmap in each block group Block allocation rule Top-level directory s inode In the empty block group, if possible Block group with maximum free inodes Other inodes and data blocks In the block group where its inode or parent resides, if possible Nearest-backside block group with free blocks more than average /usr /home /var /etc