INTRODUCTION M2488 USER’S GUIDE
1-2 CG00000-011403 REV. A April 1997
1-3.3 EDRC Compression
EDRC compression allows more data to be stored per data cartridge. Fujitsu EDRC compression is
compatible with the binary arithmetic coding algorithm, ANSI X3.225-1992, and allows interchange
of tapes with other manufacturers’ tapes that comply with this standard.
EDRC compression is comprised of two parts:
1) reblocking, which is grouping of host blocks into a single superblock and
2) compaction, which is the reduction of data stored by binary arithmetic coding.
Reblocking is always active during write operations. Compaction is selectable via the MODE
SELECT command. In this mode, host data is formed into packets consisting of a header, data, and
trailer. Packets are combined into superblocks. Normally a superblock is closed after the last packet
that causes the superblock to exceed 128 KB in length. The maximum superblock size is 451 KB in
the M2488.
Compaction reblocking (EDRC compression) is the default mode of operation for the M2488.
Reblocking is performed in the buffer (SDDP) LSI. Compaction is performed by the EDRC chip set
prior to the data buffer. Placement of compaction before the buffer effectively extends buffer capacity
by a factor equal to the average compaction rate. Compaction before the buffer also allows more effi-
cient write operation by preventing some start and stop operations resulting in fewer repositions and
better throughput.
36-track operation requires that data is always written with reblocking on. No clear data mode exists
for writing. The M2488 may read clear 18-track data however.
1-3.4 Savable Parameters
The M2488 allows changeable options, mode select page parameters, and INQUIRY vital product
data to be saved to non-volatile RAM (NVRAM) within the control unit. Refer to “SETTING
MENU” in section 4-2 for changing settable options. The MODE SELECT and CHANGE DEFINI-
TION command descriptions in the M2488 PRODUCT GUIDE contain the procedure for saving
MODE SELECT parameters and vital product data respectively.
1-3.5 Data Transfer Retry
In the event of record expansion or other compression problems, the M2488 has the ability to retry
write data transfer operations for data blocks up to 64k bytes without requesting retransmission of the
data from the initiator. This operation is automatic and is transparent to the host except for a possible
small reduction in throughput.
1-3.6 Maintenance Interface
A 9-pin (DB-9) maintenance interface (DTE device) is provided on the rear panel of the tape drive
which is used for maintenance and diagnostic operation. Nearly all maintenance and all diagnostic
capabilities are accessible through this interface.
1-3.7 Data Transfer Modes
The M2488 supports the following data transfer modes;
1) 36-Track (3490E): M2488 supports full IBM 3490E Compatible Tape operation. EDRC Com-
pacted mode is supported for read and write operations of tape. EDRC Non-compacted mode is sup-
ported for read and write operations of tape.
2) 18-Track (3480): M2488 supports read compatibility with the IBM 3480 format. It is not possi-
ble to write 3480 format tapes using the M2488 product.
EDRC Compacted mode, EDRC Non-compacted mode, and Clear mode is supported only for 18-
track read operations from tape.
3) SCSI Unique Transfers: Read and Write Buffer SCSI operations are supported by the M2488.
To Next Page
Loading...
