IBM SC34-7012-01 manual Tier 4 - active secondary site, Tier 0

Tier 0 - 3

1	2	3	4
No offsite	Truck access	Truck access	Electronic
data	method -	method and	vaulting
	tapes to	hot site
	cold site
(none)	( w e e k + )	( 1 d a y + )	( < 1 d a y )
DFSMSdss	DFSMSdss	DFSMSdss	ESCON
	DFSMShsm	DFSMShsm	Concurrent copy
	(ABARS)	(ABARS)	SMS tape

Figure 21. Disaster recovery tier 0-3: summary of solutions

The advantage of these methods is their low cost.

The disadvantages of these methods are:

vRecovery is slow, and it can take days or weeks to recover.

vAny recovery is incomplete, because any updates made after the point-in-time backup are lost.

vDisaster 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.

Chapter 19. Disaster recovery 229