Compaq Infortrend manual 12 Mixing Local and Global Spares, Logical Drive

In the example shown below, the member of Logical Drive 0 are 9 GB drives, and the members in Logical Drives 1 and 2 are 4 GB drives.

Figure 1 - 12 Mixing Local and Global Spares

Local Spare Drive	Global Spare Drive
LS
	GS
(9GB)		(4GB)

1	2	1	2	1	2
				(4GB)	(4GB)
	(9GB) (9GB)	(4GB)	(4GB)
				4	3
	3
	(9GB)			(4GB) (4GB)
Logical Drive 0		Logical Drive 1		Logical Drive 2

A Local Spare always has higher priority than a Global Spare.

It is not possible for the 4 GB Global Spare Drive to join Logical Drive 0 because of its insufficient capacity. However, using a 9GB drive as the Global Spare drive for a failed drive that comes from Logical Drive 1 or 2 will bring huge amount of excess capacity since these logical drives require 4 GB only. In the diagram below, the 9 GB Local Spare Drive will aid Logical Drive 0 once a drive in this logical drive fails. If the failed drive is in Logical Drive 1 or 2, the 4 GB Global Spare drive will immediately give aid to the failed drive.

Infortrend 1-7