CSCI 372 Computer Computer System Administration — 2 March

What is a file system

• A collection of routines in the kernel
  • proc/fs
• User view
  • open, creat, read, write, lseek
  • mkdir, rmdir
  • link, symlink
  • chmod, chown
  • mount, umount
• An on-disk format
  • FAT — linked lists
  • UFS — trees and pointers
    • inodes and directories
• extent-based file systems
  • Wasn’t this used on the mainframes?
  • Google for “ext on disk format”
  • Ext4: The Next Generation of Ext2/3 Filesystem
  • Ext4 Disk Layout
• Mounting file systems
  • initiated in user space from files similar to /etc/fstab
• What happens when the disk is corrupted?
  • What happens if you “lose” a node of a tree or linked list?
  • And how did it happen?

Backup strategies

• Why are you doing the backup?
  • Looking for the deleted file?
  • Restore after last night’s crash?
    • Is this a bare metal recovery?
    • Remember the boot blocks!
  • Answer that subpoena for discovery?
  • Clone 100 copies?
  • Moving the database?
    • This is job for the database manager
• Tools
  • dd
  • dump & restore
  • tar
  • rsync
  • partclone (clonezilla)
• Can you really get a consistent copy?
  • Suppose your system is the middle of significant upgrade
    • Isn t that like pulling the plug on a running system?
    • Will your system boot?
    • Will your web server run?
    • Will Joe Daugherty’s program compile?
  • Getting the quiet file system
    • Can you really shut down for a few hours
    • Can you take a snapshot?
      • lvcreate --snapshot
      • LVM Guide for snapshots