HP StorageWorks Virtual Array 7000 Family User and Service Guide (January 2005)

Product Overview 57
Product Overview
Operating Tips
The following information will help you understand some of the operating
features of the array and may help you manage the array efficiently.
Automatic Hot Spare Setting Behavior
The following behavior only occurs on a VA 7400/7410 operating in
AutoRAID mode, and with the hot spare mode set to Automatic. To avoid this
behavior, you may want to set the hot spare mode to a setting other than
Automatic.
The Automatic hot spare setting exhibits some unique behavior that you should
be aware of. If there are 15 or fewer disks in a redundancy group (RG), the
automatic hot spare setting reserves enough capacity to rebuild the largest disk
in the RG. When the number of disks increases to 16 or more, the array
increases the amount of capacity reserved to rebuild the two largest disks in
the array. This feature can result in the following behaviors:
■ When the 16
th
disk is added to an RG, the entire capacity of the disk will
be used to meet the increased hot spare capacity requirements. As a result,
you will not see any increase in the amount of capacity available on the
array.
■ If the 16
th
disk is of lower capacity than other disks in the RG, it may not
provide enough capacity to create the required hot spare capability. For
example, if most of the disks in the RG are 73 GB, the array will need 146
GB of capacity for hot sparing (2 X 73). If the 16
th
disk is a 36 GB disk, the
necessary capacity may not be available. In this case, a Capacity
Depletion error and a Hot Spare Unavailable error may occur.
■ If a failed disk is replaced with a disk of lower capacity, there may no
longer be enough capacity to meet the hot spare requirements. This
situation will generate a Capacity Depletion warning, indicating that there
is not enough hot spare capacity. For example replacing a failed 73 GB
disk with a 36 GB disk may cause this problem. To avoid this situation,
always replace a failed disk with a disk of the same capacity.
Install an Even Number of Disks in Each Redundancy Group
A slight increase in data availability can be achieved by managing the
number of disks in each redundancy group. Because of the manner in which
disk arrays stripe data in RAID 1+0, an even number of disks will reduce the