Hot Spare; Figure 5 Hot Spare - Fujitsu ETERNUS DX S5 Series Design Manual

2. Basic Functions
RAID Functions

Hot Spare

Hot spares are used as spare drives for when drives in a RAID group fail, or when drives are in error status.
Figure 5 Hot Spare
RAID group
Note
For RAID6-FR, because a RAID6-FR group reserves an area equivalent to one drive, data can be restored to
the reserved space even if a drive fails. If the reserved area is in use and an error occurs in another drive
(2nd) in the RAID group, then the hot spare is used as a spare.
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Types of Hot Spares
The following two types of hot spare are available:
• Global Hot Spare
This is available for any RAID group. When multiple hot spares are installed, the most appropriate hot spare is
automatically selected and incorporated into a RAID group.
Dedicated Hot Spare
•
This is only available to the specified RAID group (one RAID group).
The Dedicated Hot Spare cannot be registered in a RAID group that is registered in TPPs, FTRPs, REC Disk
Buffers, or Extreme Cache Pools.
Note
• Assign "Dedicated Hot Spares" to RAID groups that contain important data, in order to preferentially
improve their access to hot spares.
• When a drive that belongs to a RAID group for which a Dedicated Hot Spare is registered fails, the
Dedicated Hot Spare is given a higher priority than the Global Hot Spares. When a drive fails and no
unused Dedicated Hot Spares are available, a Global Hot Spare is used.
• When an Advanced Format disk is used as a hot spare, the sector format information that can be
confirmed on the server may change when used as a hot spare.
Hot spare
Failure
42 Design Guide