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Integration of Persistent Memory Data into Real-Time Asynchronous Direct Access Storage Device Remote Copy

IP.com Disclosure Number: IPCOM000118190D
Original Publication Date: 1996-Oct-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 149K

Publishing Venue

IBM

Related People

Shomler, R: AUTHOR

Abstract

Persistent data is required to recover from and resume operations following a disaster, such as a system or environmental (e.g., power) failure. Traditionally, persistent data is stored on magnetic media, such as tape and Direct Access Storage Device (DASD). Computing systems technology is evolving towards increasing use of Nonvolatile (NV) electronic Random Access Memory (RAM) memories to store some persistent data that is essential for disaster recovery. Disaster recovery often also involves a second, distant, site where copies of recovery data are maintained. Traditionally, the recovery copy is provided by point-in-time copies: "dumps" of essential data sets and DASD volumes to media, such as tape or DASD, at the distant backup site.

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Integration of Persistent Memory Data into Real-Time Asynchronous
Direct Access Storage Device Remote Copy

      Persistent data is required to recover from and resume
operations following a disaster, such as a system or environmental
(e.g., power) failure.  Traditionally, persistent data is stored on
magnetic media, such as tape and Direct Access Storage Device (DASD).
Computing systems technology is evolving towards increasing use of
Nonvolatile (NV)  electronic Random Access Memory (RAM) memories to
store some persistent  data that is essential for disaster recovery.
Disaster recovery often  also involves a second, distant, site where
copies of recovery data are maintained.  Traditionally, the recovery
copy is provided by point-in-time copies: "dumps" of essential data
sets and DASD volumes to  media, such as tape or DASD, at the distant
backup site.  However, with  a point-in-time copy, if a disaster
requires recovery at the distant site, all new data since the copy
was taken will be lost.  This has led to the use of real-time copy of
data to the distant or remote site  (also known as remote copy).  As
NV RAM system memories begin to retain  data essential to recovery,
real time copy of the NV RAM data also will  be required.

      Real-time asynchronous RAM memory copy data together with DASD
data in system recovery requires that copy of memory updates be
managed so as to be update sequence consistent with DASD copy to the
recovery site.  This is taught in (*), and is further described in
literature for  IBM's 3990 DASD Extended Remote Copy (XRC) and data
mover and other systems software.

      Merging a copy of RAM memory data with asynchronous DASD
real-time copy would be a simple extension of existing asynchronous
DASD remote copy if RAM writes could be treated as DASD writes: each
write separately captured and given a time stamp, and the resulting
captured data buffers given a virtual DASD appearance (mapping memory
addresses into DASD address space).  However, performance
characteristics of systems use of memory, make individual write
capture and time stamping  infeasible.

      A method will be described which provides a
performance-effective way to capture and merge NV memory data into a
real-time DASD asynchronous copy stream.  Much of the following
description will use terminology and structure of IBM* Extended
Remote Copy - XRC.  The ES/9000 parallel sysplex and its MVS
operating system  will be used as an example of a system that uses NV
RAM to store persistent data.  The principals described herein apply
equally to other  storages and multi-system multi-operating-system
structures.  An asynchronous remote copy operation for persistent
memory and DASD data  must meet at least two practicality tests.
First, DASD interlocks must  be minimized so that the production
system's performance is not affected.  Second, the remote copy data
mover function, such as XRC SDM,  must be able to b...