Performance Enhancement; Distributing Data And Data Striping; Data Striping - Compaq Smart Array 221 User Manual

C-10 Understanding Drive Arrays
Spare drives are automatically assigned to all volumes in an array and can be
assigned to multiple arrays connected to the same controller.

Performance Enhancement

Drive arrays allow data access performance to be dramatically enhanced over
non-arrayed drives. In addition the Smart Array 221 Controller has several other
performance enhancement features that are discussed here.

Distributing Data and Data Striping

Distributing data makes it possible to access data concurrently from multiple
drives in an array. This yields I/O rates many times faster than non-arrayed
drives. Distributing data allows data striping. See Figure C-7.
Data striping is automatically generated on an array controller in order to store
user data. A stripe is a collection of contiguous data that is distributed evenly
across all physical drives in a logical drive. The width of the stripe (the amount
stored on each physical drive) is selected to optimize the performance of the
operating system.
For example, consider an operating system that typically requests data in 32-
sector blocks. The Smart Array 221 Controller distributes the data so that the
first 32 sectors of data are on the first drive in the array. The Smart Array 221
Controller continues distributing the next 32 sectors on the second drive, the
next 32 sectors on the third drive, and so on. Evenly distributed data results in
improved performance by allowing data access to all drives simultaneously.
Writer: Karen Hale Project: Compaq Smart Array 221 Controller User Guide Comments: 388541-001
File Name: K-APPC.DOC Last Saved On: 11/5/98 1:40 PM
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