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Proper
Data Integrity
Good practices should always be followed to protect data integrity in
the physical environment include: making servers accessible only to
network administrators, keeping transmission media (such as cables and
connectors) covered and protected to ensure that they cannot be tapped,
and protecting hardware and storage media from power surges, electrostatic
discharges, and magnetism. Data integrity can also be threatened by
environmental hazards, such as heat, dust, and electrical outages and
surges.
On site Backup
Backup is the activity of copying files or databases so that they will
be preserved in case of equipment failure or other catastrophe. Backup
is usually a routine part of the operation of large businesses with
mainframes as well as the administrators of smaller business computers.
For personal computer users, backup is also necessary but often neglected.
The retrieval of files you backed up is called restoring them.
Backing up to a Tape drive
Backing up usually takes a while (about
several hours minutes for the contents of a 80 gig hard disk or array).
There are also easily removable drives that you can back up to, especially
if you have other reasons to use these (for example, for large graphic
images that you store offline). Backing up to a Zip drive, Jaz, Syquest,
or similar hard disks. Once a week or so, you should back up your working
files to an alternative storage device, such as a Zip drive.
Proper Tape Rotation
The most commonly used media rotation schedule is "Grandfather-Father-Son."
This scheme uses daily (Son), weekly (Father), and monthly (Grandfather)
backup sets.
The GFS scheme begins with the
daily backups. Typically, four backup media are labeled for the day
of the week each backs up; for example, Monday through Thursday. Each
tape is recalled for use on its labeled day. If only a one-week version
history of files is maintained, then each tape is overwritten each week.
In order to maintain a 3-week version history of files (recommended),
more tapes are required. For example this week's Monday tape will not
be overwritten for 3 weeks. Weekly backups follow a similar scenario.
A set of up to five weekly backup media is labeled "Week1,"
"Week 2," and so on. Full backups are recorded weekly, on
the day that a "Son" media is not used. Following the example
above these would be "Friday" tapes. This "Father"
media is re-used monthly. Five weekly tapes are required in order to
maintain a one-month history of files, as some months have 5 weeks.
The final set of three media is
labeled "Month1," "Month2," and so on, according
to which month of the quarter they will be used. This "Grandfather"
media records full backups on the last business day of each month. If
your backup plan follows a corporate fiscal calendar, then your monthly
tape will take the place of the week 4 or week 5 weekly/Father tape,
depending on the month. If your backup schedule follows calendar months,
then your monthly backup will vary throughout the year, replacing a
daily or weekly tape. Typically, monthly tapes are overwritten quarterly
or yearly (recommended), depending on version history requirements.
Each of these "media"
may be a single tape or a set of tapes, depending on the amount of data
to back up and the type of backup used (incremental vs. full). Weekly
and/or monthly tapes are generally pulled as archive tapes.
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On
a computer diskette or hard disk, a sector is one of the
"pies slices" the diskette or disk is divided
into. Dividing the circular medium into pie slices is a
way to organize it so that data can be located by the read/write
heads of the drive. The diskette or disk is also divided
into a number of concentric circles. Data can be located
by knowing the number of the sector and the concentric track
that passes through that sector. Each track is divided into
a number of clusters that represent the smallest unit of
storage that is addressable (can be written to or read).
Typically, a cluster is 256 or 512 bytes in length. Sector
0 of the diskette or disk contains a special file, the file
allocation table (FAT). The FAT tells where the directory
to the files on the medium is located and information about
how clusters are used. You can't look at sector 0 directly.
On hard disks, the first sector is called variously the
master boot record, the partition sector, or the partition
table. This record or table tells how and whether the disk
has been divided into logical partitions (for example, you
can divide your hard drive into two logical partitions or
drives so that you can load different operating systems
on to the disk and switch back of forth). When your operating
system is being booted or loaded into RAM, a program in
this partition sector briefly gets control, determines how
your disk is partitioned, and then reads the operating system
boot sector and gives that boot sector program control so
that the rest of the operating system can be loaded into
RAM. The partition sector is the sector that can be "infected"
when you leave a diskette in drive A that contains a boot
virus. The sectors as well as the rest of the organization
of the diskette or disk are set up as a result of the process
called formatting. |
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