Maxtor ATLAS 10K III Product Manual page 244

Feature Descriptions
• Advanced Ultra160 SCSI-LVD, Ultra320 SCSI-LVD, Ultra2-LVD, and
Ultra-SE with
68-pin wide connector or 80-pin SCA-2 connector
• Superior data integrity:
•352-bit Reed-Solomon quad-burst ECC provides fast on-the-fly
•EDC internal protection from SCSI bus to media
Many of these features are described in this chapter.
The drive contains a large, segmented buffer in RAM that is used to maximize the
throughput for sequential read streams. This cache is organized as a number of separate
track line segments. Each track line segment can hold data from one complete track
on the media, temporarily assuming the identity of the track for all input/output
functions.
The buffer is also used to combine or coalesce I/O data on a track-by-track basis,
prior to accessing the disk media. Performance is greatly improved by gathering and
combining the data on a track basis rather than on a command basis. With this unique
system, multiple commands for a particular track are coalesced in the buffer before
accessing the media.
As a result, multiple I/O commands, that address a single track are logically combined
to avoid multiple disk accesses on multiple rotations. Since most reads and writes are
sequential, this greatly increases throughput for most applications.
   2 4 ' ( ' 6 % *
The drive supports prefetch. After the controller has copied an entire media track into
a cache track line segment, a unique algorithm determines whether:
• The most recently used cache track line (track n) satisfies a read request;
• The cache memory also includes another track line (track n-1)
corresponding to the media track preceding the one that was just copied,
and;
• There is no other work currently waiting for service by the read/write
system.
If all three of these conditions are met, there is a high probability that the host will call
for data from the next media track (track n+1). So, the drive controller automatically
issues a read for that data and substitutes it for the information in the n-1 track line
segment in cache. This process, called prefetch, gives the drive a very high cache hit
rate for sequential reads.
6-2 Maxtor Atlas 10K III
correction for small errors and robust software-based correction for
larger errors