Accusys ExaRAID GUI - Manual (Page 274)

Appendix
B-5
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