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

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?

Chapter 9 Part III Linux File System Administration

The /dev Directory

List 1st floppy & 1st SCSI tape device

$ ls –l /dev/fd0 /dev/tst0

brw-rw---- 1 root floppy 2, 0 Aug 30 2001 /dev/fd0

crw-rw---- 1 root disk 9, 0 Apr 4 2001 /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

The /dev Directory

Table 6-1 (continued): Common device files

FilesystemsFilesystem• 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

Working with Floppy Disks

Table 6-3: Commands used to create filesystems

• 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

Filesystem Types

Table 6-2: Common Linux filesystems

Filesystem Types

Table 6-2 (continued): Common Linux filesystems

MountingMounting• 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


Table 6-4:Commands useful when mounting and unmounting filesystems

Mounting

Figure 6-1: The directory structure prior to mounting

Mounting

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

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


Figure 6-6: Viewing the contents of a CD-ROM in a GUI environment


Figure 6-7: Unmounting a CD-ROM device in a GUI environment

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)

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)


• 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)


• 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

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


• 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


• 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


• 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


Table 6-5:Common hard disk partition device files for /dev/had and /dev/sda


Figure 6-9: A sample Linux partitioning strategy


Figure 6-10: A sample dual-boot Linux partitioning strategy

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

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

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

Checking Filesystems for Errors

Table 6-6: Common options to the fsck command

Hard Disk Quotas

• Soft limits– Limit imposed that can be exceeded for a

certain period of time

• Hard limit– Limit imposed that cannot be exceeded

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

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

Documents

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