System information

Appendix
B-3
• Flexible hot spare policy
Hot spare disks are standby disks that are used for replacing faulty disks by rebuilding the data of the faulty disks. Spare
disks can be configured as local spare dedicated to specific disk group or global spare shared by all disk groups. Users can
also enable the auto-spare option to force the spare disk returns to standby after the faulty disks are replaced by newer disks.
This helps to control the physical organization of hard disks in the chassis.
B.5 Dynamic Configuration Migration
Business and users’ needs are dynamic, and the storage systems are required to be aligned dynamically with the business
requirements. As a result, the administrators need to reconfigure the storage from time to time. The RAID controllers are
equipped with extensive utilities for online migration of the RAID configurations while retaining the system availability. Without
the online reconfiguration utilities, unwanted system downtime and efforts for offline manual reconfiguration will stop the
administrator from optimizing the storage.
• Online disk group expansion
Expanding a disk group by adding hard disks to be its member disks enlarges the usable capacity of a disk group, and more
logical disks can be created from the disk group. An administrator can start a disk group with few hard disks and expand the
disk group later if more capacity is needed. The initial cost from disk purchase can be minimized while future expansion is
guaranteed.
• Online RAID level and stripe size migration
For performance tuning or adjusting the reliability level, the RAID level and stripe size needs to be changed. To execute the
online migration, the controller will start a background task to perform the data re-layout operations; during the migration,
RAID operations are still available to protect data and serve requests from host computers. Unlike other implementations
where only specific RAID levels or stripe sizes can be migrated, the RAID controller firmware can do the migration virtually
from all RAID levels and stripe sizes to others as long as the disk space is sufficient.
• Simultaneous migration and expansion
The RAID level migration, stripe size migration, and disk group expansion can be done simultaneously without adding extra
overheads. This significantly reduces the reconfiguration efforts and time when multiple reconfigurations are needed.
• Rebuild during RAID reconfiguration
When a disk fails during the RAID reconfiguration, the reconfiguration will be paused and disk rebuilding will be started
immediately. After the rebuilding is done, the reconfiguration will be resumed. Without rebuilding during reconfiguration, the
reconfiguration is executed on the degraded disk group, and it will take longer time to complete the reconfiguration because
large part of the data needs to be regenerated. The degradation period will be also longer, which means bad performance
and higher probability of RAID crash. It is highly advised that the administrator should ask for rebuild disk during
reconfiguration when online RAID reconfiguration is needed.
B.6 Effective Capacity Management
The spending on storage resources is rising faster than overall IT expenses, but there are still out-of-capacity emergencies.
The space of some LUNs might be used up, while there are other LUNs with idle space. The RAID controller firmware allows
the administrator to online resize the LUN capacity and easily manage the free space. Therefore, neither sophisticated
resource planning nor tedious process to do data copy and LUN re-initialization is required. The storage resources can thus
be effectively and flexibly utilized during all the life time.
• Support expansion chassis attachment
The controller is equipped with an expansion port for attaching expansion chassis. This helps to build a huge-capacity
storage solution at lower cost than to purchase multiple RAID systems. The expansion port also offers a future-proof solution
for capacity expansion that helps users to add more disk drives to a RAID system without adding switches or host bus
adapters.
• Online logical disk capacity expansion and shrink
The capacity of a logical disk can be online expanded if there is free space on its disk group. The capacity is expanded by
allocating adjacent free chunks and by relocating logical disks on the same disk group. The capacity can also be shrunk to
release free space on a disk group. During the capacity change, RAID operations are still available to protect data and serve
requests from host computers.
• Concurrent logical disk capacity and disk group expansion
The logical disk capacity expansion can also be done simultaneously with disk group expansion, and as a result, users can
expand the capacity of a LUN by adding more drives to its disk group. Without logical disk capacity expansion, the
administrator is forced to create a new LUN after the disk group expansion is done. To use the capacity on the new LUN,
either extra data management efforts like file system or application reconfiguration are needed, or the administrator needs to
deploy volume management software on the host computer, which leads to extra cost, complexity, and efforts.