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The advantage of these methods is their low cost.
The disadvantages of these methods are:
v Recovery is slow, and it can take days or weeks to recover.
v Any recovery is incomplete, because any updates made after the point-in-time
backup are lost.
v Disaster recovery is risky, and difficulties in testing your disaster recovery plan
could lead to incomplete recovery.
Tier 4 - active secondary site
Tier 4 provides a more advanced level of disaster recovery. You will lose data in
the disaster, but only a few minutes- or hours-worth.
You must assess whether the loss of data will prevent your company from
continuing in business, and what the cost of lost data will be.
Figure 22 on page 230 summarizes the tier 4 solution.
Truck access
method -
tapes to
cold site
Truck access
method and
hot site
Electronic
vaulting
No offsite
data
1234
Tier 0 - 3
(none) (week +) (1 day +) (< 1 day)
DFSMSdss DFSMSdss
DFSMShsm
(ABARS)
DFSMSdss
DFSMShsm
(ABARS)
ESCON
Concurrent copy
SMS tape
Figure 21. Disaster recovery tier 0-3: summary of solutions
Chapter 19. Disaster recovery 229