Lenovo ThinkServer RD230, Software User'S Manual

Page: 255 / 364

Creating a New Storage Configuration 8-3
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Full Initialization : A complete initialization is done on the new
configuration. You cannot write data to the new virtual drive
until the initialization is complete. This can take a long time
if the drives are large.
•
Stripe size: Stripe sizes of 8, 16, 32, 64, 128, 256, 512, and 1024
Kbytes are supported. The default is 64 Kbytes. For more
information, see the
striping Glossary entry.
•
Read policy: Specify the read policy for this virtual drive:
◊
Always read ahead : Read ahead capability allows the
controller to read sequentially ahead of requested data and
to store the additional data in cache memory, anticipating
that the data will be needed soon. This speeds up reads for
sequential data, but there is little improvement when
accessing random data.
◊
No read ahead : (the default) Disables the read ahead
capability.
◊
Adaptive read ahead : When selected, the controller begins
using read ahead if the two most recent drive accesses
occurred in sequential sectors. If the read requests are
random, the controller reverts to
No read ahead .
•
Write policy: Specify the write policy for this virtual drive:
◊
Write back : In this mode the controller sends a data transfer
completion signal to the host when the controller cache has
received all of the data in a transaction.
◊
Write through : (the default) In this mode the controller sends
a data transfer completion signal to the host when the drive
subsystem has received all of the data in a transaction.
Note: The Write Policy depends on the status of the battery
backup unit (BBU). If the BBU is not present, is bad, or is
being charged, the default Write Policy will be Write
through. This provides better data protection.
•
I/O policy: The IO policy applies to reads on a specific virtual drive.
It does not affect the read ahead cache.
◊
Cached IO : In this mode, all reads are buffered in cache
memory.