Seagate ST3285N, Руководство по эксплуатации продукта

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C.5 Caching page (08
H
)
The drive uses read look-ahead, read caching and write caching to
improve seek times and performance.
C.5.1 Read look-ahead and read caching
The drive uses an algorithm that improves seek performance by reading
the next logical sectors after the last requested sector. These unre-
quested sectors are read into a buffer and are ready to be transmitted to
the host before they are requested. Because these sectors are read
before they are requested, access read time for the sectors is virtually
eliminated. This process is called either read look-ahead or read caching.
Read look-ahead and caching are similar algorithms. Read look-ahead
occurs when a Read command requests more data than can be con-
tained in one buffer segment. Caching occurs when a Read command
requests less data than can be contained in one buffer segment.
The buffer used for read look-ahead and caching can be divided into
segments as shown in the following table. To change the number of
segments, use byte 13 of the Caching page, which is described in
Appendix C.5.3. The default is one, 256-Kbyte segment.
Number of segments Size of segment (in Kbytes)
1 256
2 128
4 64
8 32
16 16
When the buffer is divided into multiple segments, each segment func-
tions as an independent buffer, causing dramatically increased perform-
ance in multitasking and multiuser environments.
ST3655 Family SCSI Drives Product Manual, Rev. A 101