TAPE UNIT PARAMETERS

M2488 PRODUCT GUIDE

 

 

Table 5-13.

Page 10h - Device Configuration Parameters Field Description (Continued)

 

 

 

 

 

 

 

 

BYTE

 

BIT

VALUE

DESCRIPTION

 

 

 

 

 

 

 

 

 

11-13

 

 

060000h

The Buffer Size at Early Warning field indicates the value, in bytes, to which the tar-

 

 

 

 

 

 

get reduces its logical buffer size when writing between early-warning and physical

 

 

 

 

 

 

EOM.

 

 

 

 

 

 

This field is reported as not changeable on a MODE SENSE command, and the

 

 

 

 

 

 

default value is 60000h.

 

 

 

 

 

 

 

 

 

14

 

0-7

00h

When set to 00h, the Select Data Compression Algorithm field indicates that the

 

 

 

 

 

 

controller will write in EDRC uncompressed format. Uncompressed format does not

 

 

 

 

 

 

encode the customer’s data with the Binary Arithmetic Encoding hardware, but does

 

 

 

 

 

 

combine multiple customer records into a single tape block.

 

 

 

 

 

01h

When set to 01h, this field indicates that the controller will first encode customer

 

 

 

 

 

 

data using the Binary Arithmetic Encoding hardware (compress the data), and to

 

 

 

 

 

 

also combine multiple compressed customer data records into a single tape block.

 

 

 

 

 

 

NOTES:

 

 

 

 

 

 

1) It is permissible to modify the data compression algorithm mode away from BOT

 

 

 

 

 

 

and in between write operations; however, buffered write data is automatically syn-

 

 

 

 

 

 

chronized to tape prior to activating the new mode.

 

 

 

 

 

 

2) For backwards compatibility reasons, the values 83h and 84h will be accepted in

 

 

 

 

 

 

this field and treated as 00h and 01h, respectively.

 

 

 

 

 

 

 

 

5-2.7 Density Code 28h

Until now, when sending Mode Parameters with a Mode Select command, the initiator could only set 00h, 09h or 7Fh in the Density Code field in the Block Descriptor (byte 00h). The Mode Parameter data returned by a Mode Sense command would always return the value of 09h in the Density Code field. According to the ANSI SCSI-2 standard, a Density Code value of 09h referred to 18Track for- mat tape densities. The M2488 product tape drive is capable of reading both 18Track and 36Track format tapes, but will only write in the 36Track (36T) format. Since the ANSI SCSI-2 standard had not defined a Density Code value representing the 36T format, the M2483 and the early M2488 drives used Density Code 09h to represent both the 18T and 36T formats.

Since the ANSI SCSI-3 standard has defined a Density Code to represent the 36T format, the M2488 drive will now differentiate between 18T and 36T densities by using two different Density Code val- ues. Configuring feature mode bit 6 (0x40) in byte FT4 (see the M2488 User’s Guide) will cause the M2488 to associate Density Code 09h with the 18T format, and Density Code 28h with the 36T for- mat. If this feature mode configuration is not performed, the M2488 will use Density Code 09h to represent both 18T and 36T formats.

For information and instructions on configuration settings, refer to the Configuration chapter in the M2488 User’s Guide.

5-14

CG00000-011503 REV. A

April 1997

Page 250
Image 250
Fujitsu M2488 manual Density Code 28h, Eom