Download ppt - 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