AIX Guide For System Admins

AIX Backup and Restore- Part 1

2011-09-09T07:09:00.000-07:00

BACKUP and RESTORE for AIX Explained in detail.

Objectives for the module

•Understand the various different backup methods supported in AIX.
•Identify points to remember about media to use while backup, frequency of backup and type of backup.

Necessity of Backup

•Disaster Recovery Plan: Hardware failure, damages due to repair, installation, Accidental deletion
•Data is important and very expensive to recreate.
•System Image for installation
•Transfer of Data between Systems
•Long Term archive
•Before and After upgrade

Explanation:

•Backups are very much in the Disaster Recovery plan of the organization. In case there is a hardware failure, some damage to the data due to repair or installation, or due to accidental deletion, to get back the data, you need to have a backup plan.
•Data is very expensive and important. Sometimes data is far more important and expensive to replace than the hardware.
•If you are going to install a number of similar machines, system backup is one of the best options that you can have.
•One easiest way to transfer a number of files from one machine to another is to back those files onto the media and restore it on the target machine where you want to transfer the data.
•Its also recommended that before and after a system upgrade, in terms of hardware upgrade or software upgrade (operating system upgrade), its better to have a backup of your system.

Necessity of Restore

•Recover a deleted file
•Recover from a complete system crash
•Use old or archived data
•Compare versions of files

Types of Backup

Explanation:

There are mainly 3 kinds of backup. They are:-
a.System backup: In system backup, it records image backup of the whole operating system.
b.Full backup: In Full backup, it preserves all user data and configuration files.
c.Incremental backup: In Incremental backup there are 2 kinds:-
•>a. first method: Do a full backup on a particular day and rest of the week, only backup the files that have changed from the previous day. Advantage of this method of backup is, its faster but the disadvantage could be it could use up lots of tapes and if one of the tapes also is missing you may have problems to restore the data.
•>b. second method: Do a full backup on a particular day and other days take a backup of changes made since the previous full backup. This may take slightly longer time compared to the first method. The advantage is that the restoration procedure does not depend on the tape from the previous day.

Strategy for Backup

Explanation:

The above picture shows one example of a backup strategy that can be followed by an organization.

According to the slide, There is a system backup taken , then a full backup is taken on a periodic basis. Lets say on a weekly basis. On each day they may be taking an incremental backup ( either using the first method or the second method).

Devices for Backup -Floppy

/dev/fd0

One of the devices that can be used for backup is the floppy or the diskette.
This device is suitable if the size of the data that you are backing up is small.
The logical device name for the diskette drive is /dev/fdx. Most of the systems will have a single floppy disk drive so the name of the device would be mostly fd0.
There are lot of commands that can be used in AIX to work with the diskette.

They are:-
a.format command: Can be used to format a diskette. You can use the –l option with the command to format at low density.
b.flcopy command: Can be used to copy diskettes. ( diskcopycommand in DOS)
c.dosformat command: format the diskette using DOS formatting.
d.dosread: to read form the diskette (DOS diskettes)
e.doswrite: to write to a diskette (DOS diskettes)
f.dosdir: to list / view the contents of the diskette.
For all the dos related command to run, the fileset bos.dosutil has to be installed.

Devices for Backup - Tape

/dev/rmt0

•4 mm DAT
•8 mm
•1/2 – inch cartridge
•DLT

Low Capacity Retention on Open Rewind on Close

Explanation:

•The most common device used now a days for backup is the tape. There are various types of tapes available:
a.4mm DAT (Digital Audio Tape)–can hold up to 40 GB of data and transfer rate of 6 MB/sec
b.8 mm Tape–can hold up to 40 GB of data with a data transfer rate of 6 MB/sec.
c.1/4 inch cartridge: can hold up to 4 GB of data and transfer rate of 380 kb/sec
d.DLT (Digital Linear Tape)–can hold up to 70 GB at a transfer rate of 10 MB/sec
•The tape devices use the logical device name of rmtx( raw magnetic tape).
•There may be additional logical names assigned to each tape device depending on the device characteristics in terms of Write at Low Capacity, Retensionthe tape (fast forward and rewind before starting the operation) and Rewind the tape at the finish of the operation.

Devices for Backup –r / w Optical Drive

You can use JFS file system for read/write operations
You can use CD-ROM file system (cdrfs) for read only options

Explanation:

•Another device that is widely used now a days for backup is the read/write optical drive. AIX supports both, the optical drive as well as standard CD-ROM.
•The steps to access the data on the r/w optic drive like a standard read only CD-ROM drive are:-
•a. Create the file system (smit crcdrfs or crfs–v cdrfs –p ro –d <device name>)
•b. Mount the file system (mount <mount-point>)
To use the optic drive as r/w optic drive, the steps are:
Make the vg and add this device to it. (smit mkvg or mkvg –f –y vgname –d 1 device-name)
Create a file system (smit crfs or crfs –v jfs –g vgname –a size=sizefilesystem -m mountpoint –A automaticmount –p rw
•c. Mount the file system.

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We will see more about AIX BACKUP and RESTORE in Part -2 . Stay Tuned!

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Paging Space in AIX

2011-08-09T09:55:00.000-07:00

AIX Paging Space with Diagrams.

Objectives for the module

• What is Paging Space ?
• Define the requirement of Paging Space
• Maintain paging space
• Troubleshoot paging space problems

Introduction: Paging Space

Explanation:

•Virtual Memory Manager (VMM) manages paging and virtual storage related issues on your AIX.

•A running application is called as a process and these processes have to be loaded on the memory. These processes occupy 4 kb blocks on the memory called pages. As more and more processes increase on your system, the pages on the memory may not be enough for the processes to be loaded. At this juncture the inactive pages belonging to a process is moved out of the memory into the disk space called “Paging Space”, this process is called Page Out. And when-ever these inactive pages are required again by the process, they have to moved back again onto the RAM, this process is called Page In.

•The Paging Space is nothing but a area on your hard disk that contains these moved in inactive pages of the memory.

Paging Space

•Is a logical partition on the hard disk

•Acts as a temporary storage place for the “pages”

•Cannot be used as RAM

Explanation:

•Paging Space holds the inactive memory frames.

•Paging space just acts as a temporary storage area for the in-active pages and cannot be treated as a substitute for RAM. If enough memory is not available on your machine, you may get into a scenario called thrashing.

•Thrashing: Trashing is a state of paging when you do not have enough memory. When the VMM attempts to make place for a new process in the memory by moving an in-active page into the paging area, the process will need that page again in the memory wherein now VMM has to perform Page-In activity to put back the page again into the memory. Your machine is too busy only doing Page-Out and Page-In activity and no real work is done on your machine.

•In a scenario where there is thrashing, you may not be able to solve the problem just by increasing the paging space but you may have to increase your RAM to solve this problem.

Paging Space –Criteria

•Thumb rule –twice the size of RAM

•Recommendations:

–Have only one paging space per disk.

–Do not stretch paging space logical volume to spread across more than one physical volume.

–The size of paging space should be roughly same.

–Do not create paging space on a busy hard disk.

Explanation:

•Paging Space is created during the AIX installation. As a thumb rule usually the paging space is set twice of your RAM, but actually this calculation of the size of the paging space actually depends on the amount of RAM available on your system.

•If the RAM is greater than or equal to 64MB, the paging space is RAM+16 MB. If RAM is less than 64 MB, paging space is twice the size of RAM.

•When you are running low on paging space, you may get some errors like this:

Ksh: cannot fork no swap space

•At this point you will not be able to start any new processes until some processes are terminated.

Recommendations:

•Do not have more than one paging space per hard disk as paging space is allocated in a round robin manner and will use all paging areas equally. If you have two paging spaces on one disk, then you are no longer utilizing the other disks for paging activity. Do not have paging space on an already burdened hard disk. Roughly the paging spaces should be of the same size so that paging activity is balanced and faster. The paging space as a recommendation, should not span multiple hard disks.

Managing Paging Space

Use the # lsps –a command to check the paging activity.

Paging space information is stored in the file /etc/ swapspaces

Explanation:

•Monitoring the paging activity can be done with the command lsps–a.

•This command shows you the page spaces, on which hard disk they have been created, which volume group they belong to , their size, usage, whether active or not etc.

•The file /etc/ swapspaceswill hold details about the paging spaces. This file contains information about the paging areas, their logical devices names etc.

Creating a Paging space

Explanation:

•During the installation of AIX itself , system defined paging space is created. If its required you can use the smit fastpath mkps to create a new paging space

# smit mkps

•You may have to specify the volume group name where you are planning to create the paging space, size of the paging space and the hard disk on which you are planning to create it.

•You can use the option Start using this paging space NOW to activate the paging space immediately for use and you can use the option Use this paging space each time system is RESTARTED to activate the paging space at the next restart.

Modifying Paging Space settings

Explanation:

•If you want to change the settings of the paging space, you can do that by using the smit fast path chps.
#smit chps

•You can decrease the paging space or you can increase the paging space. The option of decreasing the paging space is newly added in AIX Ver5.1 and it internally uses a high level command called shrinkps o do the same.

•The system default paging space i.e. hd6 cannot be decreased below 32 MB.

Remove Paging Space

To Remove Paging space,
a. Make the paging space inactive by using the swapoff command
# swapoff /dev/paging01

b. Remove inactive paging space
# rmps paging01

Explanation:

•If you have too much of paging space and the usage is low, extra paging space can be deleted.

•Active paging spaces has to be deactivated ( which is possible dynamically from AIX Ver5.1) before you delete it.

•Swapoff command along with the paging space logical name can be used to deactivate a paging space and then you can use the rmpscommand to remove the paging space.

Problems with Paging Space

•Paging space too small:

Dynamically increase the size by allocating more partitions
chps -s LogicalPartitions PagingSpace
Example:
# chps -s 1 paging00

•Paging space too large:
Dynamically decrease the size by deallocating partitions
chps -d LogicalPartitions PagingSpace
Example:
# chps -d 1 paging00

Explanation:

•If the paging space is too small, it can be dynamically increased like any other logical volume.

•If the paging space is too large, then you can use the chpscommand to decrease the paging space.
# chps –d 2 paging01

-d 2-> delete 2 logical partitions

Paging01-> paging space name

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Working with AIX filesystem PART 3

2011-07-28T05:09:00.000-07:00

Today we shall see something about managing file-systems in IBM AIX.

Managing File Systems

Objective:

•File system integrity
•Manage/Monitor
–File system growth
–File growth
–File system space usage

How/Why Space Management ?

How ?

•Find the causes
•keep track of growing files
•check file system space usage
•check disk space

Explanation:

•If a File System reaches its full capacity, that means it cannot take any more data onto it. The filesystem size in these cases has to be increased because the file system size doesn‟t automatically increase.

•Our duty as system administrators is to use commands and techniques to find the causes for the increase in the file system size. This may involve tasks like keeping track of the growing files in the file system. Keep checking the file system space usage and decide whether to increase the size or not.

•The files that could keep growing at high speed are:

a./var/adm/wtmp-> Which keeps track of successful login information
b./etc/security/failedlogin-> which keeps track of failed login attempts.
c./var/spool-> directory which keeps cronentries, mails etc
d.$HOME/smit.log and smit.script-> smitrelated log files
e.$HOME/websm.log and websm.script-> WSM related log files
f./var/adm/sulog-> Keeps track of sucommand usage.

•Many of the above files are required files as they contain very useful information of activities going performed on the system. Completely removing them of may not be a recommended strategy but keeping eye on their increasing size and timely cropping them and removing old entries would be the maintenance task that could be done by the Administrators.

Free Disk Space

Explanation:

•You can use the dfcommand to display useful information about the statistics pertaining to the free disk information. The output of this command would show all the file systems, their sizes and out of the total size, how much is used and how much is free.

•Please refer to the man pages on df command to look at some useful options that you could use with df.

•There is also a very useful command called skulker.The skulker command is under /usr/sbin.

•The skulker command can be used to clean up the file systems by removing unwanted or old files. You can modify this skulker shell script by using an editor and configure it according to your environment.

Disk Usage

Explanation:

•The Disk Usage command (du) can be used to list the files and how many number of data blocks are utilized by them.

•If you look at the above example, the du command is giving the information of the file name, and how many number of 512 byte blocks has been allocated to that particular file. So by looking at this output you can make out as to which files are using more data blocks and take actions if required.

•du command comes with lots of very useful options like –x , -k etc. If you want more details on the various options that can be used with the du command, please look at the man pages for the same.

Control Growing Files

•/var/adm/wtmp
•/etc/security/failedlogin
•/var/adm/sulog
•/var/spool/*/*
•$HOME/smit.log
•$HOME/smit.script
•$HOME/websm.log
•$HOME/websm.script

The skulker Command

•The skulker command cleans up file systems by removing unwanted or obsolete files

•Candidate files include:
–Files older than a selected age
–Files in the /tmp directory
–a.outfiles
–corefiles
–ed.hupfiles

•skulker is normally invoked daily by the cron command as part of the crontab file of the root user

•Modify the skulkershell script to suit local needs for the removal of files

Listing Disk Usage

•The ducommand can be used to list the number of blocks used by a file or a directory

# du /home | sort -r -n
624 /home
392 /home/fred
98 /home/tom
54 /home/mary
52 /home/liz
23 /home/suzy
2 /home/guest
1 /home/steve

•To view individual file sizes, use the ls -l command.

Fragmentation Considerations

Without fragmentation
File size = 2000 bytes

With fragmentation
File size = 2000 bytes
Fragment size = 1024 bytes

Considerations to be made:
Disk space allocation
Disk space utilization
I/O activity
Free space fragmentation
Fragment allocation map

Explanation:

•In AIX the filesystem is broken into blocks called as data blocks. These data blocks by default are 4 kb in size i.e. 4096 bytes in size.

•Lets imagine you have a file called file1 which is about 1900 bytes. To store this file in the filesystem, you will require a data block (4 kb). That means file1 occupies 1900 bytes of the data block and the rest of the space in the 4 kb data block is empty. But even though rest of the space is empty, this space cannot be utilized by the file system to allocate it any other file. So in these circumstances, potentially you could have more amount of unused or wasted space.

•Here is where we can get an intro to the concept of “Fragmentation”.

•Fragmentation is a concept wherein a single data block can be broken logically into smaller fragments of size ranging from 512 bytes to 4 kb. Lets say I choose a fragment size of 1kb, that means the data block of 4 kb size is broken into 4 fragments.This would ensure that if there was a small file lets say about 1900 bytes, to store this particular file, I would potentially use up only 2 fragments of the data block and the other two fragments can be allocated to files if necessary. Thus reducing the amount of unused and wasted space in your filesystems.

Defragmenting a File System

•The defragfs command increases a file system's contiguous free space

•The file system must be mounted

defragfs [-q | -r | -s] filesystem

Options:

-q Reports the current state of the file system

-r Reports the current state of the file system and the state that would result if the defragfs command is run without either -q, -r or -s

-s Gives short report regarding the current stateof the file system

Explanation:

•Although fragmenting decreases the amount of unused or wasted space, this can actually cause some performance related problems also.

•For example: Lets imagine that the fragment size is 4 kb. There is file of 4 kb size. So 1 data block (fragment) would be assigned to the file. If I want to read this file there would be 1 I/O operating that needs to be done to read the content of the file (disk I/O happens in terms of fragment size).

•Lets say I have the same 4 kb file, but the fragment size instead of 4 kb, I‟ve changed it to 1 kb. That means to allocate space to this particular file I may require 4 1kb blocks. That means if I want to read the same file now there would be 4 disk I/O operations that needs to happen. Which would be time consuming.

•Defragmentation of the filesystemincreases the file systems contigous free space by rearranging the fragments in such a way that files get more contigousspace for allocation.

•The command:

•# /usr/bin/defragfs (-q –r ) filesystem

•can be used to report the current status of the file system and also report what would be the state of the file system after defragmentation is done.

•The file system should be mounted when you run this command.

Verify a File System

•Command syntax:

fsck [-p | -y | -n] [-f] [ file system ]

•Checks journal log

•Checks inodes, indirect blocks, data blocks, free lists

•If no file system name is specified, the fsck command checks all file systems which have the check=true attribute set in the /etc/filesystems

•Orphan files are placed in the lost+found directory

•Unmount the file system before running fsck

Complete explanation:

•File system check or fsckcan be used to verify a file system and check for its consistency. It basically checks the journal log to determine if any activity was pending, it checks the inodes, direct and indirect data block against the free lists.

•fsck command comes with lots of options:-

•-p-> stands for „preen‟. That means do not ask for any confirmation, do any minor changes required. Some people also call this option “silent” that is don‟t disturb me….

•-y-> The answer would be yes for all the questions asked during fsck

•-n-> The answer would be No for all the questions asked during fsck

•-f-> to specify the file system to conduct fsck.

•If no filesystemname is specified with the fsckcommand, all the file systems that have the option check=truespecified in the configuration file /etc/ filesystemswill be checked.

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