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Browse Prior Art Database

Management of Compressed Data in an Enterprise

IP.com Disclosure Number: IPCOM000118481D
Original Publication Date: 1997-Feb-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 115K

Publishing Venue

IBM

Related People

Goncharsky, RS: AUTHOR [+5]

Abstract

Disclosed are mechanisms to manage and dynamically control compressed data between a host and Input/Output (I/O) subsystems within an enterprise. Protocols are described to achieve a common standard for data representation, recording, and restoration, they are understood and acted on by participating software, hardware, and devices in the enterprise. These methods enable software utilities executing in the host to use the control-unit expand functions to expand host-compressed data, thus enabling early exploitation without making changes to the utility codes. These methods also enable software executing in the host to expand, using host expand function, data that was compressed by control-units on different hosts without compression facility.

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This is the abbreviated version, containing approximately 49% of the total text.

Management of Compressed Data in an Enterprise

      Disclosed are mechanisms to manage and dynamically control
compressed data between a host and Input/Output (I/O) subsystems
within an enterprise.  Protocols are described to achieve a common
standard for data representation, recording, and restoration, they
are understood and acted on by participating software, hardware, and
devices in the enterprise.  These methods enable software utilities
executing in the host to use the control-unit expand functions to
expand host-compressed data, thus enabling early exploitation without
making changes to the utility codes.  These methods also enable
software executing in the host to expand, using host expand function,
data that was compressed by control-units on different hosts without
compression facility.  These mechanisms allow for synergy and, with
recovery actions, system compatibility, when compression/expansion
functions are supported in the host, control-units, and/or devices.
The components required to present a viable implementation to achieve
this synergy are disclosed.

      A compression algorithm identifier is defined in the control
structure of the recording format, for devices that provide a
compression function transparent to the host, and which also support
removable media.  When the media is exchanged, the identifier is
detected for appropriate actions.  On devices which are capable of
accepting/transmitting compressed data from/to the host, a command
protocol is described that is used to alert the device as to the
nature of the data being handled.  The host will support an algorithm
that creates compressed data that is compatible with the I/O
subsystem algorithm, blocking factor, and the number of logical
compressors in the  I/O subsystems.  The host may also support
multiple algorithms, some of  which are not compatible with the I/O
subsystems.  The host compression  process will append a fixed-length
header to the data, containing at least a four-byte count field of
the original data, the number of logical  compactors used to compress
the data, and the blocking factor, such that  the I/O subsystem may
determine if the data being transmitted was processed with a
compatible algorithm.

      A command protocol is described to transfer compressed data
between the host and the I/O subsystem.  When the host executes a
Write-Compressed-Data (WCD) command, a data block consisting of the
header concatenated with the compressed data is transferred to the
subsystem.  The entire record is stored in packet data field.
Microcode appends an eight-byte trailer containing all zeroes and,
subsequently, the packet-data-pad and packet-data-check fields.
Modifications to the  header are described to indicate that the data
is host-compressed and that the trailer is invalid.  To read
host-compressed data back to the  host from storage device through
the I/O, the host executes a Read-Compressed-Data (RCD) command.
This c...