Promise Technology EX4650, EX8658, EX8654, EX8650 Transition, Drive Failure and Automatic Rebuild

Chapter 7: Technology Background

Because data would be lost if written to a bad sector, when a bad sector is detected, the physical drive creates a map around it. These maps are saved in the bad sector remapping table, which has a capacity of 512 reassigned blocks and 1024 error blocks.

When the table fills to a specified percentage of its capacity, PDM triggers a migration of data from the suspect drive (the physical drive with the bad sectors) to a spare drive.

During data migration, you will have access to the logical drive but it will respond more slowly to read/write tasks because of the additional operation. The time required for data migration depends on the size of the physical drive.

See “Making Background Activity Settings” on page 133.

Transition

The Transition feature enables you to specify “permanent” spare drives for your SuperTrak controller. Transition is the process of replacing a revertible spare drive that is currently part of a disk array with an unconfigured physical drive or a non-revertible spare. The revertible spare drive returns to its original status.

Transition happens automatically when the following sequence of events takes place:

•You create a revertible spare drive. “Creating a Spare Drive” on page 173.

•One of the physical drives assigned to your disk array fails and the array becomes degraded and the logical drive goes critical.

•The SuperTrak controller automatically rebuilds your array to the revertible spare drive and the array becomes functional again.

•You replace the failed physical drive with a new physical drive of equal or greater capacity.

•The SuperTrak controller automatically transitions (moves) the data from the revertible spare to the new physical drive.

•The new physical drive becomes part of the array and the revertible spare drive returns to its original spare status.

Transition happens manually when you specify a different unconfigured physical drive to transition (move) the data from the revertible spare drive.

Drive Failure and Automatic Rebuild

In the example below, there is a two-drive RAID 1 disk array.

•The physical drives in channels 1 and 2 belong to the disk array.

•The physical drive in channel 3 is unconfigured.

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