User`s guide

Chapter 1. Overview of RAID and RAID Array 200 Subsystems
EK–SWRA2–IG. C01 1–9
1.2.4.2 Write-Through caching
Write-Through caching refers to a caching policy in which the data is written to
disk before the controller acknowledges that a write operation has completed
successfully. If you choose this caching policy and there is a power failure
without battery backup, you minimize the chance of data loss.
1.2.5 Hot Swapping
Hot swapping refers to the ability, in enclosures supporting StorageWorks fault
management, to swap in a new drive as a replacement for a failed drive in a
redundant configuration, while the subsystem power is turned-on, and connected
to the system. All Digital storage enclosures, which are part of the RAID Array
200 Subsystems, support StorageWorks fault management signals.
These signals, provided on the backplanes of the shelves and supported by the
RAID controller, allow the controller to “know” when a drive fails, and when the
drive has been replaced so that automatic rebuilds occur for redundant RAID
levels.
1.2.6 Hot Spare
Hot spare refers to a drive configured into the system to automatically replace a
failed drive. If a disk fails in a redundant RAID level logical RAID drive, the hot
spare will automatically replace the failed drive and the controller will rebuild
from the remaining drives of the logical RAID drive.