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SSA RAID Adapter Installation and User's Guide.
Degraded State
C.2.5.3 Degraded State
A disk array enters the Degraded state if, while in the Exposed state, it receives a write command.
If a hot spare disk drive is enabled and available, when the first write command is sent, the array management software immediately
exchanges the missing disk for the hot spare, rebuilds the data on it, and returns the disk to the Good state.
If no hot spare disk drive is available, and a write operation is performed on the array, the disk array remains in the Degraded state
until you take action to return that disk array to the Good state. While in this state, there is an exposure to data loss if a write
operation cannot be completed because of a loss of electrical power, for example. Therefore, it is recommended that you always
have a hot spare available.
If no hot spare disk drive is available, you exchange the failed disk drive for a new one. The array management software starts a
rebuild operation to write the original data to the new disk drive from the data that is contained in the other disk drives of the array.
This action returns the disk array to the Good state.
Attention: In this mode of operation, one data check can cause the loss of a large amount of data (more than 64 KB). The array
management software must do a complete rebuild of the disk array to recover the data.
_ Copyright IBM Corp. 1996
C.2.5.3 - 1
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