Online Spares; Summary Of Raid Methods - HP ProLiant ML110 G1 User Manual

the following table can help determine which option is best for different
situations.
Table 7 Summary of RAID methods
Maximum
number of
hard drives
Tolerant
of single
hard drive
failure?
Tolerant of
multiple si-
multaneous
hard drive
failure?

Online Spares

Further protection against data loss can be achieved by assigning an
online spare (or hot spare) to any configuration except RAID 0. This hard
drive contains no data and is contained within the same storage subsystem
as the other drives in the array. When a hard drive in the array fails, the
controller can then automatically rebuild information that was originally on
the failed drive onto the online spare. This quickly restores the system to
full RAID level fault tolerance protection. However, unless RAID Advanced
Data Guarding (ADG) is being used, which can support two drive failures
in an array, in the unlikely event that a third drive in the array should fail
while data is being rewritten to the spare, the logical drive still fails.
NOTE:
For configurable storage servers, storage limitations are based on the
type of SAN to which the storage server is connected. See the individual
SAN documentation for limitations of Windows Storage Server 2003.
RAID 0 RAID 1+0
Striping Mirroring
(no fault
tolerance)
N/A N/A
Yes
No
No
If the failed
drives
are not
mirrored to
each other
HP ProLiant Storage Server user guide
RAID 5
RAID ADG
Distributed
Data
Guarding
14 Storage
system
dependent
Yes Yes
No Yes (two
drives can
fail)
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