Data backup and Recovery

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Backup & Restore
• The purpose of backup is to protect data
from loss.
• The purpose of restore is to recover data
that is temporarily unavailable due to some
unexpected event.

To backup or not to back up, that is the question.
– Backup is not free.
– No backup is risky.

Proper Backup Procedure

Choose your application
Inventory (content and media)

• Determine which data is critical.
• Determine frequency and types of backups
to be used.
– Full
– Differential
– Incremental

• Determine which data is static and which is
– Some OS installations are changed
infrequently; few backups required
– E-commerce may require continuous backups.
– Understand the changing state of your client’s
data to determine an appropriate backup sched.
– Organize with partitions

• Determine the appropriate media storage for
your backups:

Solid State?

• Partitioning of disk space is used to manage

Choose your Backup App
• Mac OS X :
– Time Machine

• Linux/Unix :
– tar (tape archive), cpio, dump

• MS Windows :
– MS Windows XP & 7 includes Backup & Restore
– Many commercial apps are available

Enterprise Level Backup Apps
• Paragon Backup & Recovery includes
customer support
• Backup4All Professional
• GRBackPro7

• Determine the categories of data so you can
schedule the backups accordingly

• Partitions are often used to manage backups
• Examples:
– The OS has its own partition and may require
infrequent backups if changes are quarterly
– User data may require nightly backups
– Users must know what partitions have backup
and the frequency (SLA).

• Full Archival Backup
– image backup implies copying the unused

• Differential Backup – what has changed
since the last backup
• Incremental Backup – what has changed
since the last backup of anytype

Full Archival Backup
• Mirror – every last bit on the disk is
• Many full backups ignore empty space.

Full Archival Backup (Pros)
• Provides a complete copy of data
• Easy to manage:
– Done less frequently than other types of
backups due to cost and resource requirements:
Monthly, Quarterly, semi-annually, annually.

Full Archival Backup (Cons)
• Usually requires more media space than
either differential or incremental.
• Takes a long time to recover the full backup
to a new disk.

Full Archival Backup
• Consider making multiple backup copies
• Full backup media should be stored offsite to
protect data from disasters
– Fire, Flood, Earthquake, Terrorist attack, Sabotage,
Hacker attacks

Full Archival Backups
• The trend is to reduce the cycle of full
backups. This is because of liability. Files
that are not backed up cannot be
• Statute may require destruction of some

Differential Backup
• Copy files changed since the last full
• Differential backups grow with time. They
can eventually grow larger than the last full
• Scheduled less frequently than a full
backups: Weekly, monthly.

Differential Backup (Pros)
• Redundancy
• Usually takes up less time and space than a
full backup.
• If the differential backup grows to the size
of the last full backup, then schedule a new
full backup.

Differential Backup (Cons)
• Redundancy – potentially many unneeded
copies of the same data.
• Subsequent differentials take longer and use
more media space.

Incremental Backups
• A backup of what has changed since the last
previous backup of any type.
• Frequency of incremental backups depends
on the client needs.
– Weekly, daily, hourly, continuously.

Incremental Backups
• Pros
– Keeps a revision history of actively changing
– Fastest backup type
– Uses the least amount of media to complete a
single backup

• Cons
– Much more difficult to manage

Schedule Example
• Full backup twice per year
• Differential each first Saturday morning of
each month that is not scheduled for a full
• Incremental each Saturday morning that is
not scheduled for a Full or Differential

Other Schedule Considerations
• Consider completing a backup in
conjunction with and before any major
system changes are scheduled.

The Actual Backup
• Assignment of responsibilities
– Written in the SA’s job description

• Acceptance of accountability
– A signed form indicating that the backup was
complete, verified and secured

The Actual Backup
• Hardware
– Choose the media type
– Centralize the backup to reduce redundancy of
– Not everyone archives the local “C-Drive” on
general purpose workstations. (SLA and user

Backup Inventory
• Inventory the backup media
– Tapes and other writable media use barcodes or
hand-written labels

• Inventory the content of the media
– The backup should have a table of contents
included in the backup

Backup Inventory
• The media label information:

System identifier
Partition name(s)
Backup category: full, differential, incremental

• The only time you know the quality of your
backup media is when you are doing a
• This is the worse time to discover you have
• Restore a small subset of random files from
the backup. Verify their integrity through
differences or checksums.

Verify: Firedrills
• When new equipment arrives, test your
backup procedure on the new equipment to
verify it works correctly

Backup Automation
• Automation reduces human errors.
• Many pre-packaged apps include automatic
• Linux/Unix backup scripts can be submitted
using the cron utility. Logs can be kept in
/var/log, and e-mail can be sent to the admin.

Secure The Backup
• Offsite storage
• Encryption: to encrypt or not to encrypt, …
– Will the encryption key always be available?
– Statute or contract (SLA) may require

Secure: Off-Site Storage
Off site storage has risks all its own
– Data can be lost/destroyed in transit
– How important is it to have a backup of the
– Some backups can be kept on site

Secure: Example Strategy
Where the backup is stored will impact
service response to restore requests:
– Consider keeping incremental backups on site.
– Differential and full backups could be stored

Data Compression
• Risks – if the media is damaged, recovery
may be difficult or impossible.
• Lossy
– some data tolerates degradation (loss of

• No-loss
– Some data should not be compressed. Know
your data!

Secure Backups
• Contract to store your data in a “secret”
offsite location. (Secret implies a need to
know basis)

Backup Considerations
• Backups slow down service. This should be
included in the SLA
– Files should be write-locked during backup.

• Avoid doing backups during peak service
hours. Schedule during early AM hours on
the weekend and holidays.

• Common reasons for restores
– Accidental file deletion
– Disk failure
– Disaster recovery
• Fire, flood, earthquake, hacker attack, sabotage,
terrorist attack, etc.

Accidental File Deletion
• If backups are once per day, lost work is limited to
one day for a given file. (RAID does not help)
• As storage technology gets cheaper by the Gbyte,
it becomes easier to implement more sophisticated
storage procedures that are more timely. (HDD
• A user wants the restoration to be immediate. The
quicker the turnaround, the happier your customer.

Disk Failure
• A disk failure causes two problems
– Loss of data
– Loss of service

• Critical systems should implement RAID so that
disk failures do not cause a loss of service.
• Restoring an entire disk is slow. Service is
hampered until the last bit is recovered.
– Consider using hot spares and hot swap

Disk Restore from Tape
• Restoring from tape can interrupt service.
• Restoring from tape slows the restore
process by a factor of about 5-10 times
compared to a simple disk to disk copy.

Tape Backup
• Large amounts of data historically favored
tape media for backup:
– Tapes are portable and fairly durable.

• Tape historically has been the preferred backup
media for very large data storage environments.
• Tape has a useful life span.
• Tape can be very robust for storage
• Easy to transport
• Some tape formats are more reliable than

Tape Inventory
• Backup tapes must be
– Properly labeled
– Properly stored

• Proper inventory is needed to do restores in
a timely fashion.
– Hand written labels are ok
– Bar codes and printed labels are better.

Tape Inventory
• Inventory is not limited to the physical tape
• The contents of tapes must be inventoried.
• The number of accesses must be logged
because tapes ware out.
– Tape equipment is not free. You don’t want to
purchase any more hardware than is needed.

• Rotate media
– Incremental backup stored on site can be

Tape Standards

DAT (4mm)

Tape Technology
• Tape technology expands in leaps.
• Tape hardware purchases are not made on a
constant basis (like disk storage).
• Tape technology is purchased in leaps.
Three year intervals are more practical.

• An occasional test of a full partition restore
is not unreasonable. This would be done if
– A change is made in the backup software
– A change of vendor for the backup software
– When a new server with new unused disk

• Without centralization, a tape drive is
needed for each server location.
• Equipment can be interchanged more easily
when centralized.

High Access DB Backups
• Some data changes so rapidly that backups
are not practical.
• RAID 1 mirroring may be the only practical
• RAID 1+1, includes a second mirror in a
RAID 1 array.

• Disk space cost drops by 1/2 about every
18-24 months.
• Disk space is filled as it expands.
• Disk requirements are increasing on a
continuous basis.
• Disk budgets increase faster than tape
backup budgets.

Backup Procedure

Choose your application
Scheduling (know your data)
The actual backup
Inventory (content and media)

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