Feature Desc riptions
6- 2 Maxt or Atl as 10K III
•Advanced Ultra160 SCSI-LVD, Ultra320 SCSI-LVD, Ultra2-LVD, and
U l tra -SE w i th
68-pin wide connector or 80-pin SCA-2 connector
•Superi or data integrity :
•352-bit Reed-Solomon quad-burst ECC provides fast on-the-fly
co rrectio n fo r sm all erro rs an d robu s t so ftwa re -b as ed co rrection for
larger errors
•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 max imize 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 assum ing the identity of the track for all input/output
functions.
The buffer is also used to combin e 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 comman ds for a particular t rack are co alesced in the buffer before
acce ssing the media.
As a result, multiple I/O commands, that address a single track are logically combined
to avoid multiple disk accesses on multiple rotatio ns. Since most reads and writes are
sequential, this greatly increase s throughput for most applications.
The drive supports prefetch. After the controller has copied an entire media track into
a cache track lin e segmen t, a unique algor ith m determines wh ether:
•The most recent ly used cache track line (track n) sat isfi es 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;
•Th ere is no othe r w o rk cu rren tly waiti n g for service b y th e re ad / w ri te
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 automat ically
iss u e s a read f or that d ata and sub s ti tu te s it for th e i nf orma tion i n th e n-1 track line
segment in cache. This process, called prefetch, gives the drive a very high cache hit
r ate fo r s e q uen ti a l re a d s .