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Smart Array Controller Technology: Drive Array Expansion and Extension
RAID migration
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The Smart Array controller webpage is available at the following URL:
http://www.compaq.com/products/servers/proliantstorage/arraycontrollers/docs/index.html
Administrators may perform volume extension in order to increase raw data
storage capacity, to improve performance by increasing the number of
spindles in a logical drive volume , or to change fault-tolerance (RAID)
configurations. With ACU or ACU-XE, an administrator can reconfigure a
logical drive to a new RAID level online, without disrupting system operation or
causing data loss. The following situations would require additional drive
space: changing RAID 0 to RAID 1, 5, or RAID ADG; or changing RAID 5 or RAID
ADG to RAID 1. Table 1 summarizes the RAID levels and the amount of space
required for each type of fault tolerance.
table 1. Summary of RAID methods
RAID 0
(striping)
Usable drive
100%
space*
Usable drive
n
space formula
Minimum
1
number of
drives
Tolerant of
No
single drive
failure?
Tolerant of
No
multiple
simultaneous
drive failures?
Read
High
performance
Write
High
performance
Relative cost
Low
*
The values for usable drive space are calculated assuming a maximum of 14
physical drives of the same capacity (or a maximum of 56 for RAID ADG) with no
online spares. HP recommends that these maximum figures (excluding any allowable
online spares) are not exceeded when configuring a drive array, due to the increased
likelihood of logical drive failure with more hard drives.
For more information about RAID levels, refer to the Smart Array Controller User
Guide, or the document titled Assessing RAID ADG vs. RAID 5 vs. RAID 1+0.
Both are available from the
RAID 1
RAID 5
(mirroring)
(distributed
data
guarding)
50%
67% to 93%
n/2
(n-1)/n
2
3
Yes
Yes
If failed
No
drives not
mirrored
to each
other
High
High
Medium
Low
High
Medium
smart array controller
RAID ADG
(advanced
data
guarding)
50% to 96%
(n-2)/n
4
Yes
yes
High
Low
medium
webpage.
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