Smart Array Controller Technology: Drive Array Expansion and Extension
8
stripe size
migration
When an administrator expands the volume capacity of an array, this does
nothing to change the stripe size of the data stored within the array. Each
RAID level has a default value designed to provide good performance across
many types of applications (see table 2). In addition, table 2 shows the range
of stripe sizes available per RAID level. If an administrator changes the RAID
level, and this new RAID level does not support the existing stripe size, the ACU
or ACU-XE changes the stripe size automatically.
table 2. Stripe sizes available per RAID level
Fault Tolerance Level
Default (KB)
Available Stripe Sizes
(KB)
RAID 0
128
8, 16, 32, 64, 128, 256
RAID 1 or 0+1
128
8, 16, 32, 64, 128, 256
RAID 5
16
8, 16, 32, 64
RAID ADG
16
8, 16, 32, 64
Certain applications, especially those that perform a majority of one type of
transaction (for example, primarily write transactions), may require tuning of
the stripe size to increase performance. Table 3 recommends stripe sizes for
general types of server applications. An administrator can take these general
recommendations and try progressively larger or smaller stripe sizes to
determine the best overall performance for a particular application. Through
ACU or ACU-XE, the administrator can make these changes online without
disruption or data loss.
table 3. Recommended stripe sizes
Type of Server Application
Suggested Stripe Size Change
Mixed read/write
Accept default value
Mainly sequential read (such as
audio/video applications)
Larger stripe sizes
Mainly write (such as image
manipulation applications)
Smaller stripes for RAID 5, RAID
ADG
Larger stripes for RAID 0, RAID 0+1,
RAID 1
conclusion
Capacity expansion simply adds drives to an array. This may improve
performance by increasing the number of spindles available. However, most
customers will want to take advantage of this newly available space by either
creating a new logical drive or extending the size of an existing one. An
administrator can also change RAID levels or stripe sizes as needed for
performance or fault-tolerance improvements. The management software
included with the Smart Array Controllers makes all these functions available
online to eliminate the need for administrators to shut down the server to
reconfigure their storage.
