1. Chapter 9 Part III Linux File System Administration
Disk devices are represented by device files that reside in the /dev directory
Device file – a file used by Linux commands that represent a specific device on the system
Character devices - Transfer data to and from the system one character or data bit at a time
Block devices
Storage devices that transfer to and from the system in chunks of many bits by caching the information in RAM
Can transfer information must faster than character devices?

2. The /dev Directory List 1st floppy & 1st SCSI tape device
$ ls –l /dev/fd0 /dev/tst0
brw-rw root floppy 2, 0 Aug /dev/fd0
crw-rw root disk , 0 Apr /dev/st0
Major number floppy 2, scsi tape 9
Used by the kernel to identify what device driver to call to interact properly with a given category of hardware
Minor number 0 on both
Used by the kernel to identify which specific device, within a given category, to use a driver to communicate with
The b indicates block devices
The c indicates character devices

3. The /dev Directory
Table 6-1 (continued): Common device files

4. Filesystems Filesystem
The organization imposed on a physical storage medium that is used to manage the storage and retrieval of data
Formatting
The process where a filesystem is placed on a disk drive
Create the ext2 format file system on floppy device 0
$ mkfs –t ext2 /dev/fd0 or
$ mkfs /dev/fd0 (ext2 is default filesystem for mkfs)
To list devices currently used on the system.
$ cat /proc/devices

5. Working with Floppy Disks
Floppy disks must be prepared before they are used in Linux
Each disk device must be formatted with a filesystem prior to being used to store files
Table 6-3: Commands used to create filesystems
Table 6-3: Commands used to create filesystems

6. Filesystem Types
Table 6-2: Common Linux filesystems

7. Filesystem Types
Table 6-2 (continued): Common Linux filesystems

8. Mounting
Mounting
Process used to associate a device with a directory in the logical directory tree such that users may store data on that device
Mount point
Directory in a file structure to which something is mounted
Mount floppy to default mount point (directory)
$ mount /dev/fd0
Mount floppy to specified mount point (directory)
$ mount /dev/fd0 /flopper

9. Working with Floppy Disks
Table 6-4: Commands useful when mounting and unmounting filesystems

10. Mounting
Figure 6-1: The directory structure prior to mounting

11. Mounting
Figure 6-2: The directory structure after mounting a floppy device

12. Mounting
When the Linux filesystem is first turned on, a filesystem present on the hard drive is mounted to the / directory
Root filesystem
Filesystem that contains the most files that make up the operating system
Should have enough free space to prevent errors and slow performance

13. Working with Floppy Disks
Figure 6-6: Viewing the contents of a CD-ROM in a GUI environment

14. Working with Floppy Disks
Figure 6-7: Unmounting a CD-ROM device in a GUI environment

15. Working with CD-ROMs
Linux systems have an ATAPI compliant IDE CD-ROM drive that attaches to the mainboard via an IDE ribbon cable
These CD-ROMs act as a normal IDE hard disk, and must be configured on of the four configurations below, as seen with their associated device files:
Primary master (/dev/hda)
Primary slave (/dev/hdb)
Secondary master (/dev/hdc)
Secondary slave (/dev/hdd)

16. Working with Hard Disks
IDE hard disk drives attach to the mainboard with an IDE cable and must be configured on one of four configurations, each of which has a different device file:
Primary master (/dev/hda)
Primary slave (/dev/hdb)
Secondary master (/dev/hdc)
Secondary slave (/dev/hdd)

17. Working with Hard Disks
SCSI hard disks are well-suited to Linux servers that require a great deal of storage space for programs and user files
Different device files associated with SCSI hard disks:
First SCSI hard disk drive (/dev/sda)
Second SCSI hard disk drive (/dev/sdb)
Third SCSI hard disk drive (/dev/sdc)

18. Working with Hard Disks
Different device files associated with SCSI hard disks (continued):
Fourth SCSI hard disk drive (/dev/sdd)
Fifth SCSI hard disk drive (/dev/sde)
Sixth SCSI hard disk drive (/dev/sdf)
And so on

19. Hard Disk Partitioning
Recall that hard disks have the largest storage capacity of any device used to store information on a regular basis
This poses some problems, because as the size of a disk increases, organization becomes more difficult and the chance of error increases
Partition
A physical division of a hard disk drive

20. Hard Disk Partitioning
It is good practice to use more than just two partitions on Linux system as this division can be useful to:
Segregate different types of data
Allow for the use of more than one type of filesystem on one hard disk drive
Reduce the chance the filesystem corruption will render a system unusable
Speed up access to stored data by keeping filesystems as small as possible

21. Hard Disk Partitioning
Tracks
Area on a hard disk that form a concentric circle of sectors
Sector
Smallest unit of data storage on a hard disk
Block
Unit of data commonly used by filesystem commands

22. Hard Disk Partitioning
Cylinder
Series of tracks on a hard disk that are written to simultaneously by the magnetic heads in a hard disk drive
Figure 6-8: The physical areas of a hard disk

23. Hard Disk Partitioning
Table 6-5: Common hard disk partition device files for /dev/had and /dev/sda

24. Hard Disk Partitioning
Figure 6-9: A sample Linux partitioning strategy

25. Hard Disk Partitioning
Figure 6-10: A sample dual-boot Linux partitioning strategy

26. Working with Hard Disk Partitions
Disk Druid is an easy-to-use partitioning tool used with Red Hat Linux, specifically designed for installation only
To create partitions after installations, you use the fdisk command
To use the fdisk command, you simply specify the hard disk partition as an argument

27. Disk Usage
There may be several filesystems mounted to the directory tree
The more filesystems that are used, the less likely it is that a corrupted filesystem may interfere with normal system operations
Conversely, using more filesystems typically results in less hard disk space per filesystem and may result in system errors if certain filesystems fill up with data
The easiest method for monitoring free space by mounted filesystem is to use the df (disk free space) command

28. Checking Filesystems for Errors
Filesystem corruption
Errors in a filesystem structure that prevent the retrieval of stored data
Syncing
Process of writing data to the hard disk drive that was stored in RAM
Bad blocks
Those areas of a storage medium used by filesystem commands

29. Checking Filesystems for Errors
Table 6-6: Common options to the fsck command

30. Hard Disk Quotas Soft limits Hard limit
Limit imposed that can be exceeded for a certain period of time
Hard limit
Limit imposed that cannot be exceeded

31. Chapter Summary
Disk devices are represented by device files that reside in the /dev directory
Each disk drive must contain a filesystem, which is then mounted to the Linux directory tree for usage using the mount command
Hard disks must be partitioned into distinct sections before filesystems are created on those partitions

32. Chapter Summary
There are many different filesystems available to Linux
It is important to monitor disk usage using the df, du, and dumpe2fs commands to avoid running out of storage space
If hard disk space is limited, you can use hard disk quotas to limit the space that each user has on filesystems