HP D3000 Disk Enclosures - Manual (Page 23)

RAID method Data redundancy Best practices Summary
characteristics over a wider range of
application workloads than RAID5. but uses the most physical disk
space. IMPORTANT: RAID1
uses about 100% more
physical disk space than
RAID0 and 70% more than
RAID5.
Striping and
parity Medium RAID 50 tolerates one drive failure
in each spanned array without loss RAID5 protects against failure
of one drive (and failure of RAID5
of data. RAID 50 requires less particular multiple drives).
rebuild time than single RAID 5 RAID 50 is a nested RAID
arrays RAID 50 requires a minimum
of six drives. method that uses RAID 0
striping across RAID 5 arrays.
Striping and
parity High RAID6 is most useful when data loss
is unacceptable but cost is also an RAID6+0 allows administrators
to split the RAID 6 storage RAID6
important factor. The probability that across multiple external boxes.
data loss will occur when an array RAID 60 requires a minimum
is configured with RAID6 is less than of eight drives. RAID 60 is a
it would be if it was configured with nested RAID method that uses
RAID5. However, write performance RAID 0 block-level striping
is lower than RAID5 because of the
two sets of parity data. across multiple RAID 6 arrays
with dual distributed parity.
With the inclusion of dual
parity, RAID 60 will tolerate
the failure of two disks in each
spanned array without loss of
data.
Striping and
parity High Organizations implementing a large
drive array should consider RAID 6 Allocates the equivalent of two
parity drives across multiple RAID6
with
because it can tolerate up to two drives and allows simultaneous Advance
simultaneous drive failures without
downtime or data loss. write operations Distributed
Data Guarding (RAID 5): Data
Guarding
(ADG)
Allocates parity data across
multiple drives and allows
simultaneous write operations.
Drive Mirroring (RAID 1 and
1+0 Striped Mirroring):
Allocates half of the drive array
to data and the other half to
mirrored data, providing two
copies of every file
Disk drive sizes and types
RAID arrays should be composed of disk drives of the same size and performance capability.
When drives are mixed within a disk enclosure, the usable capacity and the processing ability of
the entire storage subsystem is affected. For example, when a RAID array is composed of different
sized drives, the RAID array defaults to the smallest individual drive size, and capacity in the larger
drives goes unused.
Spare disks
Spares are disks that are not active members of any particular array, but have been configured
to be used when a disk in one of the arrays fails. If a spare is present, it will immediately be used
to begin rebuilding the information that was on the failed disk, using parity information from the
other member disks. During the rebuilding process, the array is operating in a reduced state and,
unless it is a RAID6 or RAID1+0 array, it cannot tolerate another disk failure in the same array. If
another disk fails at this time, the array becomes inaccessible and information stored there must
be restored from backup.
Preliminary tasks 23