UNIX OS Lecture VI

Simonas Kareiva

Vilnius University

Faculty of Mathematics and Informatics

Preparation of the material was supported by the project „Increasing Internationality in Study Programs of the Department of Computer Science II“, project number VP1–2.2–ŠMM-07-K-02-070, funded by The European Social Fund Agency and the Government of Lithuania.

Lecture VI outline

File systems

Disks

NFS protocol

RAID arrays

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Part I : file systems and disks

disk's structure and terminology

file system types

Linux file systems

indexing

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a very typical hard disk

terms:

A) Track

B) Geometrical sector

C) Sector

D) Cluster

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Clusters and sectors

Sectors make clusters

Size of a sector – 512 bytes, 2048 bytes

Sectors are grouped into clusters in order to save addressing and number of disk requests.

Cluster is the smallest logical disk’s element which can store information, so:5KB file in disk uses 8KB when cluster size is 4KB

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FAT…

FAT… bits tell the cluster address table size:

FAT12 – maximum partition Size– 32MB Max number of clusters – 2^12-12, clusters up to 8K

FAT16 – max partition size – ??? GB (exercise)Clusters up to 64K

FAT32 - (many nice features) – max partition still 2TB

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More file systems:

NTFS

UFS

EXT2

EXT3

ReiserFS

HFS

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Disk devices (Linux):

/dev/ /dev/hda

/dev/hda1 /dev/hda2

/dev/hdb /dev/hdc /dev/sda

/dev/sda1 …

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Disk devices (FreeBSD)

/dev/ /dev/ad0

/dev/ad0s1 /dev/ad0s1a /dev/ad0s1b /dev/ad0s1c

/dev/ad1 /dev/ad1s1

/dev/ad1s1a /dev/da0

/dev/da0s1 /dev/da0s1a

…

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Disk devices (Solaris)

/dev/dsk/ /dev/dsk/c1

/dev/dsk/c1t0 /dev/dsk/c1t0d0

/dev/dsk/c1t0d0p0 /dev/dsk/c1t0d0s1

c – controller (control device)

t – SCSI target

d – LUN-id (mostly 0)

s – Solaris slice or p – primary partition

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Working with disks (Linux)

# fdisk -l /dev/hdc

Disk /dev/hdc: 64 heads, 63 sectors, 787 cylinders Units = cylinders of 4032 * 512 bytes

Device Boot Start End Blocks Id System /dev/hdc1 * 1 610 1229728+ 83 Linux /dev/hdc2 611 787 356832 5 Extended /dev/hdc5 611 787 356800+ c Win95 FAT32 (LBA)

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Creating a new disk

Create a partition with fdisk (RTM)

Linux:mkfs -t ext2 /dev/hdc1

or

mkfs.reiserfs /dev/hdc1

FreeBSD:newfs /dev/da0s1a

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Mounting

mkdir /mnt/new

mount /dev/hdc1 /mnt/new

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/etc/fstab

# FreeBSD fstab:# Device Mountpoint FStype Options Dump Pass#/dev/da0s1b none swap sw 0 0/dev/da0s1a / ufs rw 1 1/dev/da0s1e /tmp ufs rw 2 2/dev/da0s1f /usr ufs rw 2 2/dev/da0s1d /var ufs rw 2 2/dev/da1s1a /squid ufs rw 2 2/dev/acd0 /cdrom cd9660 ro,noauto 0 0

# Linux fstab:/dev/rootvg/lv00 / ext3 defaults 1 1/dev/rootvg/lv02 /vz ext3 defaults 1 2/dev/md0 /boot ext3 defaults 1 2tmpfs /dev/shm tmpfs defaults 0 0devpts /dev/pts devpts gid=5,mode=620 0 0sysfs /sys sysfs defaults 0 0proc /proc proc defaults 0 0/dev/rootvg/lv01 swap swap defaults 0 0

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NFS protocol

Like Windows File Sharing, but not exactly...

Designed for intensive data exchange between servers

Easily configurable

From an OS point of view, its just another file system (partition)

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What you’ll need:

FreeBSD:nfsd – daemon, processing user requestsmountd – daemon, responsible for FS mounting rpcbind – additional service used for chatting within

the network

/etc/exports:Format:

/folder/which/shared –paremeters client1 client2…

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/etc/exports:

/cdrom -ro host1 host2 host3/home -alldands 10.0.0.2 10.0.0.3 10.0.0.4/a -maproot=root host.example.com box.example.org/usr/src /usr/ports host4

Then we execute:

# rpcbind # nfsd -u -t -n 4 # mountd -r

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Or use:# showmount -e serverExports list on server:/usr 10.10.10.0/a 10.10.10.0

# mkdand /mnt/a

# mount server:/a /mnt/a# df -F nfs Filesystem Type blocks use avail %use Mounted on server:/a nfs 68510 55804 12706 81% /mnt/a

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Practical uses

Most OS’s support installation through NFS, its enough to have 1 DVD which is shared via NFS on LAN.

By using NFS you can create a couple of HTTP servers with the same content and distribute traffic between them by using the round-robin load balancing algorithm.

In large networks, it is useful to keep /home folders on NFS, so that user’s files are saved centrally.

Exercise: think of more practical NFS uses!

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RAID

terms:RAID – Redundant array of Inexpensive Disks JBOD – Just a bunch of … ?Hot spare – reserve playerStripe – data distribution in multiple devicesMirror – data backup in multiple devices Parity – protection from errors system (XOR):

0 XOR 0 = 0 0 XOR 1 = 1 1 XOR 0 = 1 1 XOR 1 = 0 Dedicated parity – data in separate disk

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RAID types

RAID0, RAID1, RAID2, RAID3, RAID4, RAID5, RAID6

RAID0+1, RAID1+0, RAID0+3, RAID51, …

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Say,

We have four disks:Three 200GB disksOne 300GB disk

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RAID0

Size = n * min ( 200GB, 300GB ) = 800GB

Advantages:Fast readingFast writingLots of space

Disadvantages:Totally unreliable (if one of the disks

breaks down, the entire RAID stops)

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RAID1

Size= min ( 200GB, 300GB ) = 200GB

Advantages:Fast readingReliability and security

Disadvantages:Expensive writing (to both disks)

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RAID5

Size= n-1 * min ( 200GB, 300GB ) = 200GB

Advantages:Fast readingFast writingReliability and security (parity)

Disadvantages:Requires at least 3 disks, often requires +1

additionalSlow, when at least stripe size is being written

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Parity

disk #1: -------- (Data)disk #2: -------- (Data)disk #3: -------- (Data)disk #4: -------- (Data)disk #5: -------- (Hot Spare)disk #6: -------- (Parity)

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Parity

disk #1: 00101010 (Data)disk #2: 10001110 (Data)disk #3: 11110111 (Data)disk #4: 10110101 (Data)disk #5: -------- (Hot Spare)disk #6: -------- (Parity)

00101010 XOR 10001110 XOR 11110111 XOR 10110101 = 11100110

D1 XOR D2 XOR D3 XOR D4 = ( (D1 XOR D2) XOR D3) XOR D4

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Parity

disk #1: 00101010 (Data)disk #2: 10001110 (Data)disk #3: 11110111 (Data)disk #4: 10110101 (Data)disk #5: -------- (Hot Spare)disk #6: 11100110 (Parity)

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Parity

disk #1: 00101010 (Data)disk #2: 10001110 (Data)disk #3: --Dead-- (Data)disk #4: 10110101 (Data)disk #5: 11110111 (Hot Spare)disk #6: 11100110 (Parity)

00101010 XOR 10001110 XOR 11100110 XOR 10110101 = 11110111

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RAID2, RAID3

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RAID derivatives32

Yo, dawg, I heard you like RAID…

… so we put more RAID into your RAID so that you can have more RAID!

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Cheat-sheet of RAID configurations

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