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Global Status Device State Machine (GSDSM) Disclosure Number: IPCOM000015892D
Original Publication Date: 2002-May-01
Included in the Prior Art Database: 2003-Jun-21
Document File: 2 page(s) / 59K

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Global Status Device State Machine

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Global Status Device State Machine (GSDSM)

Global Status Device State Machine

A program is disclosed which allows global data to be stored on a disk subsystem where the data will not be lost due to a single point of failure or power failure. The state machine in Figure 1 details the program method which allows a dynamic response to disk failures and provides a recovery method to restore the global status data following a power failure. The restoration of the global status data is executed during a machines initial microcode load in order to provide the data required in recovering the previous operating state of the machine. The two methods described in the Global Status Device State Machine are Establish and Reassign.

Figure 1


Config data read successful

Config data read


Read devices named

in config data

Match version IDs of config data to device data

Establish complete

Establish failed

New device

Remove device from

candidate list

Set Reassign_Pending


Write Request

Check for lock


Write Config

Data failed

Add device to candidate list


Device status change

Device deleted

New primary or secondary device

At least 1 write successful

Config data read failed

Both reads failed

At least 1 device

read successful

No match

New device state

New config

Pick any 2 devices


Write ConfigCheck version ID


Increment version ID


Scan device candidates

for the best 2

Write GS data to


Version ID


No devices available

There are two types of data mentioned in Figure 1, config data and global status data. The config data contains information which points a storage subsystem to the devices storing the global status data, and it contains the version Id of the most recent copy of the global status data. The global status data itself includes a version Id and the data required to restore a machine to its previous operating state.

An establish (Figure 1) is executed during the initial microcode load of a machine where two redundant copies of the config data are read from locations on separate failure boundaries. The version Ids on the copies are compared to determine the most recent version. The latest copy of the config data points to the devices which store the global status data, and it contains the versi...