D-12
Understanding Drive Arrays
Writer: Pamela King Project: SMART-2DH Array Controller Reference Guide Comments: 295469-002
File Name: K-APPD.DOC Last Saved On: 2/27/98 12:06 PM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
Performance Enhancement
Drive arrays allow data access performance to be dramatically enhanced over
non-arrayed drives. In addition the SMART-2DH 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.
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-2DH Controller distributes the data so that the
first 32 sectors of data are on the first drive in the array. The SMART-2DH
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 in an
array improves performance by allowing access to all drives simultaneously.
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