HP StorageWorks Virtual Array 7000 Family User and Service Guide (January 2005)
Table Of Contents
- Warranty Information
- Product Overview
- System Configurations
- Lowest Entry Point, Non-HA Minimum Configuration (VA 7100 only)
- Lowest Entry Point, Non-HA Minimum Configuration (VA 7410)
- Entry Level Non-Cluster With Path Redundancy (All VA arrays)
- Entry Level Cluster with Path Redundancy High Availability (VA 7410)
- Midrange Non-Cluster (All VA arrays)
- Midrange Non-Cluster (VA 7410)
- Midrange Non-Cluster with Full Storage Path Redundancy (All VA Arrays)
- Typical Non-Clustered with Path Redundancy (VA 7410)
- Typical Clustered Configuration (All VA models)
- Typical Clustered Configuration (VA 7410)
- HP-UX MC Service Guard or Windows 2000 Cluster (All VA arrays)
- Highly Redundant Cluster (VA 7410)
- Typical Highly Redundant Cluster (All VA models)
- Typical Highly Redundant Cluster (VA 7410)
- Troubleshooting
- Servicing & Upgrading
- Specifications & Regulatory Statements
Product Overview 47
Product Overview
RAID Levels
Redundant Array of Inexpensive Disks (RAID) technology uses different
industry-standard techniques for storing data and maintaining data
redundancy. These techniques, called “RAID levels”, define the method used
for distributing data on the disks in a logical unit (LUN). LUNs that use different
RAID levels can be created in the same array.
The virtual array can be operated in RAID 1+0 level or AutoRAID level, which
is a combination of RAID 1+0 and RAID 5DP. The RAID level selected is
influenced by factors such as capacity demands and performance
requirements. Once a RAID level is selected, it is used for the entire array.
Changing the RAID Level of the Array
The RAID level for the array is established during installation. It is possible to
change the RAID level after installation. The steps involved in changing the
RAID level depend on which mode you are changing to.
■ Changing from RAID 1+0 to AutoRAID. The RAID level can be changed
from RAID 1+0 to AutoRAID on-line. However, it is recommended that you
backup all data on the array before changing the RAID level.
■ Changing from AutoRAID to RAID 1+0. The RAID level cannot be
changed from AutoRAID to RAID 1+0 on-line. This change requires a
complete reformat of the entire array, which will destroy all data on the
array. Before changing from AutoRAID to RAID 1+0, backup all data on
the array for restoration after the format and RAID change are complete.
RAID 1+0
RAID 1+0 provides data redundancy and good performance. However, the
performance is achieved by using a less efficient technique of storing
redundant data called “mirroring”. Mirroring maintains two copies of the data
on separate disks. Therefore, half of the disk space is consumed by redundant
data — the “mirror”. RAID 1+0 also stripes the mirrored data segments across
all the disks in a RAID Group. A read can use either copy of the data; a write
operation must update both copies of the data.
Figure 18 is an example showing the distribution of the two copies of data in a
RAID 1+0 configuration. This example shows one RAID Group with 10 data
segments, each data segment has an associated mirror segment. After a
single disk failure, the copy of a segment is always is available on another disk
— this disk(s) is referred to as the “adjacent disk(s)”. The array will continue
operation without data loss in the event of any non-adjacent disk failure.