NEC Express5800/A1080a, User Manual, Page: 335 / 696

Hardware
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Virtual Disk
Virtual disk is a logical drive defined in disk group. It is recognized as a physical drive by OS. The
allowable number of virtual disks is up to 16 per disk group, or up to 64 per controller.
The figure below shows a sample configuration in which the RAID Controller (MegaRAID) is
connected with three HDDs, creating one Disk Group. Two RAID5 virtual disks (VD) are defined
in the Disk Group.
Parity
The parity means redundant data. A single set of redundant data is created from the data saved
in more than one HDD.
The created redundant data is used for data recovery when a HDD is defected.
Hot-Swap
The hot-swap enables a HDD to be removed (or replaced) under system operation.
Hot Spare
The hot-spare is prepared as an auxiliary HDD substituting for a defected HDD included in a disk
group which is configured at a redundant RAID level. Detecting a HDD fault, the system
disconnects the HDD (or makes it offline) and starts rebuild using the hot-spare.
NOTE:
For standby rebuild (rebuild using hot-spares), refer to "Features
of RAID Controller (MegaRAID)".