HP SureStore E Disk Array 12H User's and Service Manual (C5445-90901, September 1999)

Concepts and Management
Disk Array Hardware
97
Concepts
Figure 23. Installing a Second High-Capacity Disk
Disk Stamps
Because data is distributed across all disks, the array controller must keep track of which disks are installed
in the array. To do this, the array controller writes a unique stamp on each disk. The disk stamp includes a
unique number assigned to the disk (typically its serial number), and the numbers of the other disks in the
disk set. This information allows the array controller to determine if any disk is missing from the disk set.
The disk stamp identifies each disk’s “logical” position in the array configuration relative to the other disks.
When managing data, the array controller deals in terms of logical position, rather than physical location in
the array enclosure. Thus, disks can be moved to different enclosure slots without any impact on array
operation. As long as the correct disks are installed, the array controller is satisfied.
When another disk is installed in the array enclosure, the array controller checks the disk stamp to
determine if the disk is new or if it was previously installed in another array. In the latter case, the array
controller assumes there may be some valuable data on the disk and does not include it (even
automatically) until you tell it explicitly to do so. Once included, the disk is given a new stamp indicating it
now belongs to the array’s disk set.