User Guide

AMD-RAIDXpert2 User Guide
53987 Rev. 3.01 June 2016
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Arrays, Disks and RAID Levels
Chapter 3
For additional information, see Section 6.6.13, Add or Remove Dedicated Spares, on page 82.
3.12 Global Sparing
A global spare is a disk that is assigned as an alternate disk for multiple arrays, instead of
associating it with only one array.
Many arrays can be restored using the global spare disk, as long as it is not already part of the
array and it has enough space available. Unlike a dedicated spare, this type of spare can be
assigned at any time, even while tasks are running on arrays.
Assigning a disk for use as a global spare does not reserve space on that disk. An automatic restore
is not guaranteed if a disk fails.
If there is not enough disk space on the global spare, make room for the fail-over to complete, or
assign a different disk with enough capacity as the spare. If there is enough space available on the
global spare and a disk failure occurs, the restore process starts automatically.
For additional information, see Section 6.6.14, Add or Remove Global Spares, on page 83.
3.13 RAID Performance Considerations
With RAID technology, performance is based on the following considerations:
 The number and organization of disks in an array.
 Caching attributes used for the array.
 Application workload.
3.13.1 Number and Organization of Disks
RAID functions increase performance by putting more disks to work and by buffering data for the
host.
Many disks can transfer data at greater than 100 MB per second. RAIDXpert2 can aggregate this
bandwidth in an almost linear fashion, as more of the same disks are included in an array.
3.13.2 Caching Attributes
Arrays can also be configured to provide read and Write Back caching using RAIDXpert2, if
desired. Write Back caching has a large effect on most workloads, but should be used with
caution.