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High availability

• Global Hot Spares

A Global Hot Spare is an unused online available drive, which is

ready for replacing the failure disk. The Global Hot Spare is one

of the most important features that SAS RAID controllers provide

to deliver a high degree of fault-tolerance. A Global Hot Spare

is a spare physical drive that has been marked as a global hot

spare and therefore is not a member of any RAID set. If a disk

drive used in a volume set fails, then the Global Hot Spare will

automatically take its place and he data previously located on the

failed drive is reconstructed on the Global Hot Spare.

For this feature to work properly, the global hot spare must have

at least the same capacity as the drive it replaces. Global Hot

Spares only work with RAID level 1, 10, 3, 5, 6, 30, 50, or 60

volume set. You can configure up to three global hot spares with

SAS RAID controller.

The “Create Hot Spare” option gives you the ability to define

a global hot spare disk drive. To effectively use the global hot

spare feature, you must always maintain at least one drive that is

marked as a global spare.

• Hot-Swap Disk Drive Support

The SAS RAID controller chip includes a protection circuit that

supports the replacement of SAS/SATA hard disk drives without

having to shut down or reboot the system. A removable hard

drive tray can deliver “hot swappable” fault-tolerant RAID solutions.

This feature provides advanced fault tolerant RAID protection

and “online” drive replacement.
 

• Auto Declare Hot-Spare

If a disk drive is brought online into a system operating in degraded

mode, the SAS RAID controllers will automatically declare

the new disk as a spare and begin rebuilding the degraded

volume. The Auto Declare Hot-Spare function requires that the

smallest drive contained within the volume set in which the failure

occurred.

In the normal status, the newly installed drive will be reconfigured

an online free disk. But, the newly-installed drive is automatically

assigned as a hot spare if any hot spare disk was used

to rebuild and without new installed drive replaced it. In this

condition, the Auto Declare Hot-Spare status will be disappeared

if the RAID subsystem has since powered off/on.

Important:

The hot spare must have at least the same capacity as the

drive it replaces.

The Hot-Swap function can be used to rebuild disk drives in arrays

with data redundancy such as RAID level 1, 10, 3, 5, 6, 30,

50 and 60.

• Auto Rebuilding

If a hot spare is available, the rebuild starts automatically when

a drive fails. The SAS RAID controllers automatically and transparently

rebuild failed drives in the background at user-definable

rebuild rates.

If a hot spare is not available, the failed disk drive must be replaced

with a new disk drive so that the data on the failed drive

can be automatically rebuilt and so that fault tolerance can be

maintained.

The SAS RAID controllers will automatically restart the system

and rebuilding process if the system is shut down or powered off

abnormally during a reconstruction procedure condition.

When a disk is hot swapped, although the system is functionally

operational, the system may no longer be fault tolerant. Fault

tolerance will be lost until the removed drive is replaced and the

rebuild operation is completed.

During the automatic rebuild process, system activity will continue

as normal, however, the system performance and fault tolerance

will be affected.
 

• Adjustable Rebuild Priority

Rebuilding a degraded volume incurs a load on the RAID subsystem.

The SAS RAID controllers allow the user to select the rebuild

priority to balance volume access and rebuild tasks appropriately.

The Background Task Priority is a relative indication of how much

time the controller devotes to a background operation, such as

rebuilding or migrating.

The SAS RAID controller allows user to choose the task priority

(Ultra Low (5%), Low (20%), Medium (50%), High (80%)) to balance

volume set access and background tasks appropriately. For

high array performance, specify an Ultra Low value. Like volume

initialization, after a volume rebuilds, it does not require a system

reboot.