NonStop Systems Introduction

Transaction Management

NonStop Systems Introduction—527825-001

5-12

File Recovery

You have seen that TMF volume recovery provides a quick, handy solution to the

problem of multiple transaction failures resulting from a hardware failure. But in certain

cases, volume recovery cannot be used to recover from the effects of a hardware

failure. For example, the failure of an unmirrored disk or the failure of a pair of

mirrored disks can destroy the contents of database files and make the files unusable.

Why can’t volume recovery be used to recover from such failures? Remember that

volume recovery uses the current version of the database on disk as the starting point

of recovery. It reapplies successful transactions to this database and backs out

unsuccessful transactions. But if the disks containing the current version of the

database are damaged, volume recovery has nothing to work with. The operations

staff must use file recovery instead.

Figure 5-7 on page 5-13 shows how file recovery uses online dumps and audit dumps

to restore the warehouse database after a dual media failure (the failure of a pair of

mirrored disks). For the sake of simplicity, the figure shows only one member of the

mirrored disk pair.

Online dumps are tape or disk copies of the database. The operations staff makes

these archive copies on a regular basis: for example, daily or weekly. An archive copy

is a copy of the database as it existed at some point in the past. Archive copies are

saved for recovery purposes in case the current copy of the database is damaged or

lost.

Figure 5-6. TMF Volume Recovery

Sales office

Headquarters

Warehouse

power outage

Audit trail

Warehouse

power restored

Audit trail

Databases

VST061.vsd