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The 3490-A20 is a 36-track, 2 Control Unit component for an IBM 3490
tape subsystem. The IBM 3490 Enhanced Capability (3490E) Model A20 Control
Unit supports the Models B20 and B40 Tape Drive Units. The A20 provides
granularity from a minimum 2x2 (A20 x B20) configuration to a maximum
2x16 (A20 x Four B40s) configuration. Standard features include: Improved
Data Recording Capability, an 8 Mb buffer, Dual Communications Capability,
and improved utilization of ES Connection* (ESCON*) adapters providing
new possibilities in performance, connectivity, and remote tape operations.
There are two 36-track control unit functions and one power supply in
each Model A20 control unit. The approximate doubling of the cartridge
capacity over the IBM base 3490s is introduced via a 36-track bidirectional
Enhanced Capability tape format. This cartridge capacity improvement reduces
tape cost, as the number of cartridges required for all multiple volume
data sets is reduced by up to half. Archive, backup, master file, and
interchange data all require fewer cartridges for the same amount of data.
Total tape mounts are reduced, cartridge handling and cartridge library
space are reduced, and the data capacity of the cartridge loader is doubled.
In MVS the "LOCATE" function will accommodate the new format, and depending
on the location of the requested record, LOCATE may be faster than with
previous formats and can never take longer than a LOCATE to the physical
end of tape.
An instantaneous data rate of up to 9 MB/second is provided through the
performance enhancement function which is standard on each control unit.
With the performance enhancement function, subsystem throughput of up
to 23 percent improvement can be achieved on parallel channels in environments
with long string lengths and uncompacted or low compacted (IDRC) data.
The performance enhancement function has a significant effect on subsystem
throughput when using ESCON Channels and can show dramatic improvement
(up to 69 percent) with high (IDRC) compaction ratios. Your IBM representative
has access to detailed performance data showing a comparison between a
3490 subsystem prior to the addition of the performance enhancement function,
and a 3490 subsystem with the performance enhancement function. Relative
improvement with both parallel and ESCON Channels is shown. The subsystem
effective data rate is improved, reducing the backup and batch window
time constraints, and reducing the time required for master file creation
and use.
Expanded utilization of ESCON Channels (including ESCON Directors) provides
new possibilities in floor-space planning, configurability, and connectivity.
An A20 Control Unit (fully configured with ESCON adapters) provides up
to 128 logical paths to ESCON Host processors, when ESCON Directors are
employed in the system configuration.
Through the use of ESCON Directors, ESCON channel connected 3490Es can
be installed up to 23 kilometers (14.3 miles) from the host, addressing
remote tape operations requirements, and providing remote site security
advantages. Because tape operations are more efficient, tape drive growth
may decrease, and in some cases, fewer drives may be required. The 3490
Enhanced Model A20 writes the new tape format introduced with this product
and, for ease of migration, will read all 3480 and 3490 IBM Cartridge
System Tape formats. When service is required, devices are serviced from
the rear of the subsystem while the remainder of the subsystem remains
operational. Reliability and availability are improved by advanced electronic
packaging: the number of electronic cards within the control unit are
reduced by half over 3490 base models. Higher reliability of circuit technology,
and the micro code input disk unit, and enhanced Control Unit error recovery
procedures (ERP) all contribute to improved reliability. Up to four channel
adapters per control unit function may be installed. These can be parallel
adapters, ESCON adapters, or combinations of both.
Growth Enablement
The Enhanced Capability Model A10 provide the additional granularity
and lower cost 1X2 (A10 X B20) configuration required for entry into the
high-end 3490, and can be upgraded later to the A20. In addition, the
customer can add B20s and/or B40s up to a maximum configuration of 2X16
(A20 X four B40s). Mixing of parallel adapters and ESCON Adapters is allowed.
Both adapter types can be field or factory installed.
The improved performance of these 3490E models reduces the amount of
time required to save or restore data to direct access storage devices
(DASD), resulting in higher availability of production data to users.
The performance enhancement function for the A20, with an 8MB buffer
and increased speed compactor, will improve subsystem performance on both
parallel channels and ESCON channels. This "no cost" upgrade includes
a new micro-code load that provides improved autoblocking that increases
cartridge capacity and performance. Autoblocking is always invoked; IDRC
invoked is considered normal operations. IDRC can be turned off, via software
only, for special requirements (such as writing tape labels). The performance
enhancement function is announced as part of the A20.
A control unit reliability and availability improvement was made by reducing
14 cards to 7 cards, providing room for up to four ESCON Adapters per
control unit function, further enhancing connectivity.
Unique microcode and host software are required to support this product.
Configurations
The Model A20 can support up to 4 Model B40 or up to 4 Model B20 or 3
Model B40 plus 1 Model B20 or 2 Model B40 plus up to 2 Model B20 or 1
Model B40 plus up to 3 Model B20. All Model B20s must be last in all mixed
configurations.
Devices Supported
- 3490 Model B20
- 3490 Model B40
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