Conner CFP4207 Series, Руководство по эксплуатации продукта

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Drive Operations Chapter 3
Technical Reference Manual Page 25
Read Retention On (Read Retention Priority = 0 or F):
The interface processor initiates a full segment read of 253 sectors (FD
H
blocks)
to the background processor. There are three different situations which would
be considered a cache hit on a subsequent read.
•
Full: All of the data requested is transferred from the buffer segment and
retained.
•
Partial: Some but not all of the data is cached in a buffer segment. If the
cached data is in the Active Segment and the remaining data is part of the
full segment read, the drive will transfer the requested data from the buffer
as the background process fills it. If the cached data is in the Active
Segment but the remaining data is not part of the full segment read, the
drive will turn off read retention until the next Active Segment miss occurs
and issues a new read (forever) to the background process. This allows the
drive to adapt to long sequential reads even in read retention mode. If the
data is part of an Inactive Segment, a new full segment read is initiated,
making this the Active Segment.
•
Potential: If none of the data is in the Active Segment, but is part of the
full segment read, the drive will transfer the data as it becomes available.
Read Retention Off (Read Retention Priority = 1): The interface processor
initiates a "read forever" command to the background processor and the buffer
segment is treated as a circular buffer which is back filled as sectors are
transferred to the host. There are three different situations which would be
considered a cache hit on a subsequent read.
•
Full: All of the requested data is cached in a buffer segment. If it is the
Active Segment, the data will be transferred to the host and refilled with
next sequential data. If the data in an Inactive Segment, the data is
transferred to the host and retained.
•
Partial: This is when some, but not all of the data is cached in a buffer
segment. If the data is in the Active Segment, data is transferred to the host
as the background process fills the buffer and the "read forever" is allowed to
refill the buffer. If the data in an Inactive Segment, the cached data is
transferred and a new read operation is initiated for the remaining data,
making this the Active Segment.
•
Potential: None of the data is cached. The active segment is checked and if
the requested data is within 63 sectors of being read, the drive will allow the
"read forever" operation to continue and the data is transferred to the host
when it is available.