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Understanding stripe-unit size
With RAID technology, data is striped across an array of physical drives. This
data-distribution scheme complements the way the operating system requests data.
The granularity at which data is stored on one drive of the array before subsequent
data is stored on the next drive of the array is called the stripe-unit size .
You can set the stripe-unit size to 8 KB, 16 KB, 32 KB, or 64 KB. You can maximize
the performance of your ServeRAID controller by setting the stripe-unit size to a
value that is close to the size of the system I/O requests. For example,
performance in transaction-based environments, which typically involve large
blocks of data, might be optimal when the stripe-unit size is set to 32 KB or 64 KB.
However, performance in file and print environments, which typically involve
multiple small blocks of data, might be optimal when the stripe-unit size is set to
8 KB or 16 KB.
The ServeRAID-7t, ServeRAID-8i, ServeRAID-8k/8k-l, and
HostRAID controllers do not support an 8 KB stripe-unit size. The ServeRAID-7t
ServeRAID-8i, and ServeRAID-8k/8k-l controllers support these additional
stripe-unit sizes: 128 KB, 256 KB, 512 KB, and 1024 KB.
The collection of stripe units, from the first drive of the array to the last drive of
the array, is called a stripe.
After you configure an array and store data on the logical drives, you
cannot change the stripe-unit size without destroying data in the logical drives.
You can set the stripe-unit size to 8 KB, 16 KB, 32 KB, or 64 KB. The default setting
is 8 KB data bytes.
v When the stripe-unit size is 8 KB or 16 KB, the maximum number of physical
drives in an array is 16.
v If you have a ServeRAID-3H or ServeRAID-3HB controller using ServeRAID
firmware (version 4.0, or later) and the stripe-unit size is 32 KB or 64 KB, the
maximum number of physical drives in an array is 16. Otherwise, when the
stripe-unit size is 32 KB or 64 KB, the maximum number of physical drives in an
array is 8.
v If you have a ServeRAID-4 controller and the stripe-unit size is set to 32 KB or
64 KB, the maximum number of physical drives in an array is 16.
More information
v Changing the stripe-unit size (action)
v Application environment groups reference
Understanding enabled and disabled read-ahead cache mode for
logical drives
Note: You can enable and disable the read-ahead setting without destroying data
in a logical drive by using the ServeRAID Manager in bootable-CD mode.
Enabled read-ahead cache mode
The controller transfers data from the logical drive to its local cache in increments
equal to the stripe-unit size. This provides excellent overall performance when
194 ServeRAID Manager Installation and User's Guide