Fault Tolerance and Disaster Recovery

Topics

• Using Antivirus software• Fault tolerance

– Power– Redundancy– Storage– Services

• Disaster Recovery– Backup/Restore– Offsite storage– Hot and Cold spares– Hot, warm, and cold sites

Assessing Fault Tolerance and Disaster Recovery Needs

• A proper disaster recovery plan encompasses planning and preparing for a network disaster, but also recovering from it.

• A disaster is anything that destroys data or attempts, either deliberately or accidentally, to impair network operation.

• Disaster recovery is often taken too lightly and many administrators come to regret it.

Prepared for Disaster

• Hot site• Warm site• Cold site

Hot Site

• In a hot site, every computer system and piece of information has a redundant copy.

• This level of fault tolerance is used when systems must be up 100 percent of the time.

• Hot sites are strictly fault-tolerant implementations, not disaster recovery.

Two Levels of Clustering

• Failover Clustering– Active and passive servers– Uses a heart beat to detect failure

• Advantages and Disadvantages

• True Clustering– Supports multiple devices– Provides load balancing

• Advantages and Disadvantages

Fault Tolerance

One system fails, one takes overOne system fails, one takes over

100% of clients100% of clients

Warm Site

• In a warm site, the network service and data are available most of the time.

• The data and services are less critical than those in a hot site.

• The most commonly used warm-site technology is a duplicate server.

• This is Disaster Recovery not fault-tolerance

Cold Site

• A cold site cannot guarantee server uptime.

• If a server fails, the IT personnel will do their best to recover and fix the problem

Power Management

• Surge Protectors• Battery Backup• Line Conditioners• Power management is for fault

tolerance

Surge Protectors

• Level of Protection– Only covers Over-voltage– Common Components

• Active Protection Light• Site Wiring Fault Light• Ground• IEEE 587 Category A (ANSI/IEEE

C62.41) Let-Through• UL Listing• Circuit Breaker• Additional Ports

Battery Backup

• Battery backup systems protect computer systems from power failures.– Under-Voltage

• Brown outs• Black outs

– Two Main Types of Battery Backup• Standby Power Supply• Uninterruptible Power Supply

Standby Power Supply

• Power is supplied from the AC unit• Battery is backup only• Uses a micro-switch to change power

sources in the event of a power failure– They may include:

• Surge protection• Multiple outlets• Line voltage indicator• Batter power indicator• System management port

Uninterruptible Power Supply

• Power is supplied through the battery• Batteries must be replaced regularly

– They may include:• Multiple outlets• Line voltage indicator• Batter power indicator• System management port

Line Conditioners

• Dirty power introduces noise in the system.

• This can cause many types of problems, including – random lockups, – random reboots, and – system crashes.

Disk System Fault Tolerance

• Mirroring• Duplexing• Data striping• Redundant Array of Independent (or

Inexpensive) Disks (RAID)

Partitions

Primary partitionsPrimary partitions

Extended partition with logical drives

Extended partition with logical drives

Physical diskPhysical disk CCCC

DDDD

E F GE F GE F GE F G

RAID

Data written to multiple disksData written to multiple disks

Data can be restored if one disk fails

Data can be restored if one disk fails

Striping (RAID 0)

Data

DDDD AAAA TTTT AAAA

Mirroring or Duplexing (RAID 1)

Disk controllersDisk controllers

Data

DATADATADATADATA DATADATADATADATA DATADATADATADATA DATADATADATADATA

Data

Drive 0 Drive 1 Drive 0 Drive 1

MirroringMirroring DuplexingDuplexing

Striping with Parity (RAID 5)

Data

DDDD

DDDD

DDDD

DDDD

ParityParityParityParity

ParityParityParityParity

AAAA

DDDD

AAAA

AAAA

ParityParityParityParity

TTTT

AAAA

AAAA

TTTT ParityParityParityParity

AAAA

TTTT

TTTT

TTTT

ParityParityParityParity

AAAA

AAAA

AAAA

AAAA

Backup Considerations

• Backup Media Options• Small-Capacity Removable Disks• Large-Capacity Removable Disks• Removable Optical Disks• Magnetic Tape

Backup Policies

Backup policy

Testing

Hardware and media

Administration

Software

The Standard Procedure for Database Backup

Procedure for backing up a database:1. Take database offline2. Back up the database files3. Clear the circular logs4. Put the database back online

Standard Procedure for Database Restoration

Procedure for restoring a database:1. Take database offline2. Restore database from latest tape3. Put database back online and do not

allow clients to connect4. Play back the circular logs5. Allow users to connect

Data Backups

Your company’s last line of defenseConsiderations:

What value does the data have?How will the backup be stored?

TapeDiskCloud

What procedure will be used?

Backup Media Types

TapesTapes Hard disksHard disks CD- and DVD-ROMsCD- and DVD-ROMs Cloud servicesCloud services

Backup Types

FullFullDifferentialDifferential IncrementalIncremental

Full backupFull backup

Am

ou

nt

of

da

ta

Am

ou

nt

of

da

ta

100%

50%

Am

ou

nt

of

da

ta

1 2 3 4 5

1 2 3 4 5 1 2 3 4 5

100%

50%

100%

50%

FullFull

Backup Types

Type What is Backed up

Archive Bit Cleared?

Number of sets to restore

Full All Data Yes Full only

Differential Since Last Full Backup

No Full plus Last differential

Incremental Since Last Backup

Yes Full plus every daily incremental to the last Full backup

Monthly tapes: 12 plus 1 extra

Daily tapes: 4 for Mon – Thur, plus 1 extra Weekly tapes: 4 Fridays, plus 1 extra

The GFS Rotation Method

The Tower of Hanoi Rotation Method

Day

Me

dia

Se

t

Media Set

Used Every

A 2 days

B 4 days

C 8 days

D & E

16 days alternating between set D and E

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

A A A A A A A A

B B B B

C C

D

E

Maintaining a Data Backup System

Backup maintenanceMaintain the data integrity

Test your backups

Maintain your hardwareInspect tapesClean drives

Data Backup System Maintenance

• Verify backups• Test restoration• Review logs• Replace tapes on

schedule• Maintain tapes and tape

drives• Clean tape drives• Replace damaged tapes

Backing Up Remote Users and Workstations

1. Must be online and powered up2. Remote users may require a

method of backup that allows them to back up from the road

3. Consider Web-based backups

Specialized Data Backups

Enterprise backupsMobile usersPower userworkstations

Open files Database Email

Virus Protection

• Types of Viruses– File Viruses– Macro Viruses– Boot Sector Viruses– Hoax Virus

Updating Antivirus Components

• A typical antivirus program consists of two components:– The definition files– The engine

Scanning for Viruses

• Two types of antivirus scans:– On-demand– On-access

Software Revisions

Is It Necessary? Where to Get PatchesHow to Apply Patches

Summary

• Summary• Exam Essentials• Review Questions