Table of Contents
Advertisement
Chapter 8. Split-Site Management
This chapter describes how to configure and manage a system in which the computing
and disk drive resources are split between two or more sites, so that the system can
continue to operate if one site is lost.
Configuration of RAID-1 and RAID-10 Arrays
RAID-1 and RAID-10 arrays hold data on mirrored pairs of disk drives; that is, the two
disk drives of a particular pair contain the same data. If either disk drive fails, the data
is still available. This characteristic of these array types allows the mirrored copies of
the data to be held on disk drives that are in different domains. For example, the disk
drives can be in different disk subsystems, or on different sites. If one domain loses
power, the array continues to operate because one copy of the data is still available.
The RAID manager ensures that the two copies of the data are synchronized. It is
possible for an array to become split in half, and for the adapters to become unable to
communicate with each other. The design of the system must include precautions,
therefore, that prevent both using systems from continuing to operate on the half of the
array that each system can access. Such a condition causes the data on each mirrored
pair to be inconsistent. The RAID manager allows only one half of the array to remain
available. This action prevents two using systems writing different data to the separate
halves of the array.
The Split Array Resolution flag determines whether the primary or secondary side of the
array can operate when some of the configuration disks are not available. Normally, the
Split Array Resolution flag is reset. When the Split Array Resolution flag is reset and the
secondary configuration disk can be accessed, but no primary configuration disk drive
can be accessed by an adapter, the array goes into the Offline state to that adapter.
Note: In the ssaraid command, the Split Array Resolution Flag is known as
When the Split Array Resolution flag is set and the secondary configuration disk drive
can be detected, access to the array is permitted. If the Split Array Resolution flag is
set, and the secondary configuration disk cannot be detected, the array goes into the
Offline state.
The Split Array Resolution flag affects initialization of the array:
v If an array appears with the Split Array Resolution flag set, only member disk drives
from the secondary half of the array are accepted. If member disk drives from the
primary half of the array appear, they are exchanged into the array and a rebuilding
process begins. These actions are logged for each primary disk drive. If all the
member disk drives for the primary half of the array appear, and they are rebuilding,
or they have completed rebuilding, the Split Array Resolution flag is reset.
v If, in a RAID-10 array, the first two primary disk drives and the first secondary disk
drive are all in separate power domains, you can configure that array so that it can
always continue to operate after a power failure of a single power domain. After the
split_resolution.
193
Advertisement
Table of Contents
