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Planning, Installing, and Managing the IBM System x3950 M2
Ahead: This enables read ahead capability, which 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.
Adaptive: When Adaptive read ahead is selected, the controller begins
using read ahead if the two most recent disk accesses occurred in
sequential sectors. If the read requests are random, the controller
reverts to Normal (no read ahead).
•
Write Policy: Specify the write policy for this virtual drive:
WBack
:
In Writeback mode the controller sends a data transfer
completion signal to the host when the controller cache has received all
the data in a transaction. This setting is recommended in Standard
mode.
WThru: In Writethrough mode the controller sends a data transfer
completion signal to the host when the disk subsystem has received all
the data in a transaction. This is the default.
Bad BBU: Select this mode if you want the controller to use Writeback
mode but the controller has no BBU or the BBU is bad. If you do not
choose this option, the controller firmware automatically switches to
Writethrough mode if it detects a bad or missing BBU.
•
IO Policy: The IO Policy applies to reads on a specific virtual disk. It
does not affect the read-ahead cache.
Direct: In direct I/O mode, reads are not buffered in cache memory.
Data is transferred to the cache and the host concurrently. If the same
data block is read again, it comes from cache memory. This is the
default.
Cached: In cached I/O mode, all reads are buffered in cache memory.
•
Disk Cache Policy: Specify the disk cache policy:
Enable: Enable the disk cache.
Disable: Disable the disk cache. This is the default.
Unchanged: Leave the current disk cache policy unchanged.
•
Disable BGI: Specify the background initialization status:
Leave background initialization enabled with set to
No
.
•
Select Size: Specify the size of the virtual disk in megabytes.
By default the size is set to the maximum allowed size defined by the
RAID level at this virtual disk. You can specify a smaller size if you want
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