CSC414 “Introduction to UNIX/ Linux” Lecture 3

Schedule 1. Introduction to Unix/ Linux 2. Kernel Structure and Device Drivers. 3. System and Storage Structure. 4. Processes and Inter- Process Communication. 5. Shell Programming. 6. User Management and Disk Quota. 7. System Management. 8. Network Management. 9. Security. 10. Advanced System Administration. 2015Qassim University, College of Computer, 9th level 2

Contents: Disks Types Storage Hardware Interfaces Storage management layers Overview Disk Partitioning. RAID: Redundant Arrays of Inexpensive Disks. Logical Volume Management. Linux filesystems: the ext family Boot Loader. 2015Qassim University, College of Computer, 9th level 3

Disks Types:  Hard disks A typical hard drive contains several rotating platters coated with magnetic film. They are read and written by tiny skating heads that are mounted on a metal arm that swings back and forth to position them. 2015Qassim University, College of Computer, 9th level 4

Cont.  Solid state disks SSDs spread reads and writes across banks of flash memory cells, which are individually rather slow in comparison to modern hard disks. But because of parallelism, the SSD as a whole meets or exceeds the bandwidth of a traditional disk. The great strength of SSDs is that they continue to perform well when data is read or written at random, an access pattern that’s predominant in real-world use. 2015Qassim University, College of Computer, 9th level 5

Storage Hardware Interfaces ATA (Advanced Technology Attachment), known in earlier revisions as IDE, was developed as a simple, low-cost interface for PCs. It was originally called Integrated Drive Electronics because it put the hardware controller in the same box as the disk platters and used a relatively high-level protocol for communication between the computer and the disks. 2015Qassim University, College of Computer, 9th level 6

Cont. Serial ATA, SATA.. In addition to supporting much higher transfer rates (currently 3 Gb/s, with 6 Gb/s soon to arrive), SATA simplifies connectivity with tidier cabling and a longer maximum cable length. SATA has native support for hot-swapping and (optional) command queuing. 2015Qassim University, College of Computer, 9th level 7

Cont. Small Computer System Interface, SCSI, is one of the most widely supported disk interfaces. It supports multiple disks on a bus and various speeds and communication styles. In the past it was used for disks, tape drives, scanners, and printers, but these days most peripherals have abandoned SCSI in favor of USB. 2015Qassim University, College of Computer, 9th level 8

Storage management layers:  A storage device is anything that looks like a disk.  It can be a hard disk, a flash drive, an SSD, an external RAID array implemented in hardware.  The exact hardware doesn’t matter, as long as the device allows random access, handles block I/O, and is represented by a device file. Partition. RAID array. Volume groups and logical volumes. Filesystem 2015Qassim University, College of Computer, 9th level 9

Partition fixed-size subsection of a storage device. Each partition has its own device file and acts much like an independent storage device. For efficiency, the same driver that handles the underlying device usually implements partitioning. Most partitioning schemes consume a few blocks at the start of the device to record the ranges of blocks that make up each partition. Reduce the risk of system failure in case a partition becomes full. Encapsulate your data. Since file system corruption is local to a partition, you stand to lose only some of your data if an accident occurs. 2015Qassim University, College of Computer, 9th level 10

Partition Fields Device: This field displays the partition's device name. Start: This field shows the sector on your hard drive where the partition begins. End: This field shows the sector on your hard drive where the partition ends. Size: This field shows the partition's size (in MB). Type: This field shows the partition's type (for example, ext2, ext3, or vfat). Mount Point: A mount point is the location within the directory hierarchy at which a volume exists; the volume is "mounted" at this location. This field indicates where the partition will be mounted. 2015Qassim University, College of Computer, 9th level 11

Cont. Unless you have a reason for doing otherwise, it is recommended that you create the following partitions: /boot partition – contains kernel images and grub configuration and commands / partition /var partition /home partition Any other partition based on application (e.g /usr/local for squid) swap partition — swap partitions are used to support virtual memory. In other words, data is written to a swap partition when there is not enough RAM to store the data your system is processing. The size of your swap partition should be equal to twice your computer's RAM. 2015Qassim University, College of Computer, 9th level 12

Cont. IDE Disk Partitions /dev/hda (Primary Master Disk) /dev/hda1 (First Primary Partition) /dev/hda2 (Second Primary Partition) /dev/hdb (Primary Slave Partition) /dev/hdb1 /dev/hdc (Secondary Master/Slave Partition) /dev/hdc1 SCSI Disk Partitions /dev/sda1, /dev/sda2 /dev/sdb1, /dev/sdb2 /dev/sdc1, /dev/sdc2 2015Qassim University, College of Computer, 9th level 13

RAID: Redundant Arrays of Inexpensive Disks combines multiple storage devices into one virtualized device. Depending on how you set up the array, this configuration can increase performance (by reading or writing disks in parallel). Increase reliability (by duplicating or parity-checking data across multiple disks). RAID can be implemented by the operating system or by various types of hardware. As the name suggests, RAID is typically conceived of as an aggregation of bare drives, but modern implementations let you use as a component of a RAID array anything that acts like a disk. 2015Qassim University, College of Computer, 9th level 14

Logical Volume Management 2015Qassim University, College of Computer, 9th level 15 These systems aggregate physical devices to form pools of storage called volume groups. The administrator can then subdivide this pool into logical volumes in much the same way that disks of yore were divided into partitions. Since the LVM adds a layer of indirection between logical and physical blocks, it can freeze the logical state of a volume simply by making a copy of the mapping table.

Cont. 2015Qassim University, College of Computer, 9th level 16 Logical volumes are more flexible and powerful than disk partitions. Here are some of the magical operations a volume manager lets you carry out: Move logical volumes among different physical devices Grow and shrink logical volumes on the fly Take copy-on-write “snapshots” of logical volumes Replace on-line drives without interrupting service Incorporate mirroring or striping in your logical volumes

Linux filesystems: the ext family. The “second extended filesystem,” ext2, was for a long time the mainstream Linux standard Ext3 adds journaling capability to the existing ext2 code, a conceptually simple modification that increases reliability enormously. Even more interestingly, the ext3 extensions were implemented without changing the fundamental structure of ext2. In fact, you can still mount an ext3 filesystem as an ext2 filesystem—it just won’t have journaling enabled. Ext4 is a comparatively incremental update that raises a few size limits, increases the performance of certain operations. The on-disk format is compatible enough that ext2 and ext3 filesystems can be mounted as ext4 filesystems. Furthermore, ext4 filesystems can be mounted as if they were ext3 filesystems provided that the extent system has not been used. 2015Qassim University, College of Computer, 9th level 17

Boot Loader In order for the BIOS to load an OS it looks for instructions on the first sector of a hard drive. On the first sector of the hard drive resides the master boot record (MBR), and is where a boot loader is initialized. Depending on the boot loader, additional files may be stored and read from a partition on the hard drive. After this step the boot loader begins to start the operating system, and is not used again until the next boot. 2015Qassim University, College of Computer, 9th level 18

Reading Chapter 8 form “ Unix® and Linux® System Administration Handbook, Fourth Edition” 2015Qassim University, College of Computer, 9th level 19