Conner CFP2105 series, Руководство по эксплуатации продукта, Страница: 30 / 90

Chapter 3 Drive Operations
Page 22 Filepro CFP2105 Series
Data Error Correction
The drive uses a three way interleaved 96-bit Reed-Solomon code to perform
error correction. An additional 48-bit Cyclic Redundancy Code (CRC) provides
additional miscorrection detection. For each 512-byte block, the on-the-fly error
correction polynomial is capable of correcting:
•
one error burst of up to 41 bits in length
•
two error bursts each up to 17 bits in length
The miscorrection probability is less than 1 bit in 10
24
bits transfered.
Downloadable Microcode
The SCSI interface code is split into two parts which are designated as ROM or
RAM code. The ROM code contains the basic SCSI operating code and code to
support commands such as INQUIRY, TEST UNIT READY, REQUEST SENSE,
START/STOP UNIT, etc., which may have to be responded to prior to the drive
being in a ready state. The part of the interface code referred to as RAM code
resides on an area of the disk which is reserved to the drive and is not directly
accessible through the interface. This code is referred to as RAM code because it
is read from the disk and is loaded into static RAM after power is applied to the
disk, as soon as the drive is able to read from the disk.
The RAM code consists of a resident portion which is loaded after a Power On
Reset. Two different versions of RAM code overlays also reside on the disk. The
read look ahead code overlay is the default and is loaded into RAM during the
initial power-on. If a Queue Tag message is received by the drive, the drive will
execute the command and while it is in Status Phase, will read the Queuing code
overlay from the disk and load it into the RAM. This operation takes about 600
milliseconds, after which the drive will complete the command by sending the
status. The drive will continue to operate with Queuing code residing in RAM
until the next Power On Reset.
Refer to the next section for a discussion of the buffer management implications
for the different RAM codes.
The RAM code may be upgraded on the disk via the factory serial port or
through the interface using the WRITE BUFFER command. Refer to the
WRITE BUFFER command in the Eleventh Generation SCSI Interface Manual
for a discussion of the procedure.