Transcript A Big Test Result - Knowledge Systems Institute

Introduction to
Computer Networks
Avoiding Data Loss
This lesson presents an overview of the possible
causes of data loss and how to protect the
network against them.
Data Protection
• The causes of a network disaster inlude:
• Component failure.
• Computer viruses.
• Data deletion and corruption.
• Theft and vandalism.
• Fire caused by arson or electrical mishaps.
• Natural disasters, such as lightning, floods
earthquakes.
• Power-supply failure and power surges.
Data Protection & Recovery
• There are several ways to prevent or recover from
data loss, including:
• Tape backup systems.
• An uninterruptible power supply (UPS).
• Fault-tolerant systems.
• Optical drives and disks.
Tape Backup
• The simplest, most inexpensive way to avoid
disastrous loss of data is to implement a schedule
of periodic backups with storage offsite.
• Using a tape backup is still one of the few simple
and economical ways to ensure that data remains
safe and usable.
• A secure backup strategy minimizes the risk of
losing data by maintaining a current backup—
copies of existing files—so that files can be
recovered if harm comes to the original data.
Implementing a Backup System
• Complete backups make restoring disk configuration
much easier, but can require multiple tapes if there
are large amounts of data.
• Backing up individual files and directories might
require fewer tapes, but could require the
administrator to manually restore disk
configurations.
• Critical data should be backed up according to
daily, weekly, or monthly schedules, depending on
how critical the data is and how frequently it is
updated.
Testing and Storage
• Experienced administrators test the backup system
before committing to it.
• They perform a backup, delete the information,
restore the data, and attempt to use the data.
• The administrator should test the backup
procedures regularly to verify that what is
expected to be backed up is actually being backed
up.
Maintaining a Backup Log
• Maintaining a log of all backups is critical for later
file recovery.
• A copy of the log should be kept with the backup
tapes, as well as at the computer site.
• The log should record the following information:
•
Date of backup,
Tape-set number
Type of backup performed
Which computer was backed up
Which files were backed up
Who performed the backup, etc.
Installing the Backup System
• Backing up across the network is the most efficient
way to back up multiple systems.
• Network
traffic is
reduced by
backing up
to a
separate
segment.
Uninterruptible Power Supply (UPS)
• An UPS is an automated external power supply
designed to keep a server or other device running in
the event of a power failure.
• The standard UPS provides a network with two
crucial components:
• A power source to run the server for a short time
• A safe shutdown management service
Fault-Tolerant Systems (1)
• Fault-tolerant systems protect data by duplicating
data or placing data in different physical sources,
such as different partitions or different disks.
• Data redundancy allows access to data even if part
of the data system fails.
• Fault-tolerant systems should never be used as
replacements for regular backup of servers and loca
hard disks.
Fault-Tolerant Systems (2)
• Fault-tolerant systems offer these alternatives for
data redundancy:
• Disk striping
• Disk mirroring
• Sector sparing
• Mirrored drive arrays
• Clustering
Redundant Array of Independent
Disks (RAID) (1)
• Fault-tolerance options are standardized and
categorized into levels. These levels are known as
redundant array of independent disks (RAID):
• Level 0—Disk Striping
Redundant Array of Independent
Disks (RAID) (2)
• Level 1—Disk
Mirroring
Redundant Array of Independent
Disks (RAID) (3)
• Level 2 — Disk Striping with ECC
• When a block of data is written, the block is
broken up and distributed (interleaved) across all
data drives.
• Error-correction code (ECC) requires a larger
amount of disk space than parity-checking
methods, discussed under Level 3.
Redundant Array of Independent
Disks (RAID) (3)
• Level 3—ECC Stored As Parity
• Disk striping with ECC stored as parity is similar to
level 2.
• The term parity refers to an error-checking
procedure in which the number of 1s must
always be the same—either odd or even—for
each group of bits transmitted without error.
• In this strategy, the ECC method is replaced
with a parity-checking scheme that requires
only one disk to store parity data.
Level 3—ECC Stored As Parity
Redundant Array of Independent
Disks (RAID) (4)
• Level 4—Disk Striping with Large Blocks
• This strategy moves away from data interleaving
by writing complete blocks of data to each disk in
the array.
• The process is still known as disk striping, but
is done with large blocks. A separate check disk
is used to store parity information.
• Each time a write operation occurs, the
associated parity information must be read from
the check disk and modified.
Level 4—Disk Striping with Large
Blocks
Redundant Array of Independent
Disks (RAID) (5)
• Level 5—Striping with Parity
• The data and parity information are arranged so
that the two are always on different disks.
• A parity stripe block exists for each stripe (row)
across the disk.
• The parity stripe block is used to reconstruct
data for a failed physical disk.
• Striping with parity is currently the most popular
approach to fault-tolerant design.
Redundant Array of Independent
Disks (RAID) (6)
• Level 10—Mirrored Drive Arrays
• RAID level 10 mirrors data across two identical
RAID 0 drive arrays.
Redundant Array of Independent
Disks (RAID) (7)
• Sector Sparing
• This feature automatically adds sector-recovery
capabilities to the file system while the computer
is running.
Microsoft Clustering
• Microsoft Clustering is Microsoft's implementation
of server clustering.
• The term "clustering" refers to a group of
independent systems that work together as a single
system.
• Should a system within the cluster fail, the cluster
software will disperse the work from the failed
system to the remaining systems in the cluster.
Optical Drives and Disks
• In optical technology, data is stored on a rigid disk
by altering the disk's surface with a laser beam.
• As the technology evolves from the original readonly and read-write CD-ROMs to the new DVD
technologies, these devices are being used more
and more to store large amounts of retrievable data
• Optical-drive manufacturers provide a large array
of storage configurations that are either networkready or can be used with a network server.
Disaster Recovery
• The best way to recover from a disaster is to
prevent it from happening in the first place.
• Not all disasters can be prevented.
• When considering disaster protection, you will
need a plan for hardware, software, and data.
• Physical components of a network can be easily
replaced and are usually covered by some form of
insurance, but data is highly vulnerable to disaster.