Seagate HAWK 4, Product Manual

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14 Product Manual - Hawk 4 Family SCSI-2 (Volume 1), Rev. F
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5.6 Caching write data
Write caching is a write operation by the drive that makes use of a drive buffer storage area where the data to
be written to the medium is stored in one or more segments while the drive performs the write command.
Write caching is enabled along with read caching. For write caching, the same buffer space and segmenta-
tion is used as set up for read functions. The buffer segmentation scheme is set up or changed independently,
having nothing to do with whether or not read and write caching is enabled or disabled. When a write com-
mand is issued, the cache is first checked to see if any logical blocks that are to be written are already stored
in the cache from a previous read or write command. If there are, the respective cache segments are cleared.
The new data is cached for subsequent Read commands.
If the number of write data logical blocks exceeds the size of the segment being written into when the end of
the segment is reached, the data is written into the beginning of the same cache segment, overwriting the
data that was written there at the beginning of the operation. However, the drive does not overwrite data that
has not yet been written to the medium.
Tables 11.3.2-1 and 11.3.2-2 show Mode default settings for the Hawk 4 family of drives.