IBM Debuts GRS, A New Data Replication Service in the Cloud

IBM Debuts GRS, A New Data Replication Service in the Cloud

November 16, 2022

Alex Woodie

If you run your IBM i workloads in the IBM Cloud, there is a new data replication offering available that could help you recover more quickly from a disaster. Dubbed Global Replication Services (GRS), the offering is only available for Power Systems Virtual Server customers running in two IBM data centers at the moment. But IBM says GRS could eventually be used with on-prem Power and FlashSystem deployments, too.

GRS, which IBM introduced in a September 22 blog post, provides asynchronous data replication for IBM i, AIX, and Linux data, as well as failover and failback mechanisms. The offering was designed to replicate a customer’s PowerVS storage volume from one IBM data center to a geographically distant IBM data center, as part of a replicated pair.

GRS is based in part on the data replication mechanism used in IBM’s Spectrum Virtualize, the software for managing IBM FlashSystem SAN arrays (and before that, the Storwize arrays), according to Tom Mathews, a distinguished engineer from IBM’s Austin lab who has worked on GRS.

“For very long time we’ve had global replication capabilities on-prem between two controllers,” Mathews tells IT Jungle. “It’s very similar. The magic here, though, was getting this to work in a multi-tenant” environment.

Multi-tenancy is important because it guarantees customers a level of storage isolation when running in IBM Cloud, Mathews says. In an on-prem Spectrum Virtualize environment, there wasn’t as much of a need for customers to conduct security validation to ensure that the secondary system has access to data when failover and failback mechanisms are put into action, he says.

But such controls are necessary in a shared multi-tenant environment in the cloud, and it took a bit of work by IBM to make it work, Mathews says. IBM built GRS on PowerVS so that it works “just like” Spectrum Virtualize does on prem,” he says.

“PowerVS is fundamentally a multi-tenant solution,” Mathews says. “You can have – I’m just making names up – Coke and Pepsi on the same systems, both doing replication. That’s why it’s significant.”

This has been the top request by PowerVS customers, says Ming Christensen, a director of product management who works out of the Austin lab.

“Customers want it,” she says. “They’ve been doing single-tenant private cloud environments for many generations. They want this enterprise capability in Power Virtual Server in a multi-tenant environment.”

While GRS may get additional capabilities over time, it provides a complete DR solution at this point in time, Mathews says. “It’s a complete solution,” he says. “We really don’t have any follow on work to do right now, except for maybe polishing a few things that we discovered late at the end. But you don’t have any extensive enhancements that we have planned.”

IBM says customers can wrap additional capabilities around GRS to provide a high availability solution. For example, since it’s a storage volume-based data replication system, it doesn’t know anything about IBM i objects, Mathews says. For application high availability, it would need to be paired with other software.

IBM is encouraging its customers to tape Technology Services (formerly Lab Services) and its business partners to build additional capabilities around GRS.

“That’s why we bring various capabilities to inject into the solution, inject into the products, so the customer can have an end-to-end solution,” Christensen says. “They can do it themselves, or work with our services or their preferred partner to put all these solutions together. And I think next year we’ll work on more . . . of an end-to-end solution.”

Currently, only two IBM Cloud data centers are supported with GRS, including DAL1 3, which is based in Dallas, Texas, and WDCO 4, which is based in Washington D.C. IBM plans on bringing GRS to more IBM Cloud data centers over time, Mathews says.

IBM recognizes that customers want to run in multiple architectures, including hybrid cloud setups that utilize servers and storage in on-prem and cloud data centers. IBM is working to accommodate those customers with GRS, but there are challenges, Mathews says.

“That’s a bit problematic because we don’t have control of their . . . storage,” he says. “We have to have complete control of the storage to do this safely and reliably, including the storage and the security elements around this storage and so forth.”

IBM is currently working to deliver cloud-native PowerVS in private cloud environments, via its Power Private Cloud as a service offering. GRS could potentially be included in that, Mathews says. “That’s something that we’re working on,” he says. “It’s not something we have right now.”

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Input/Output Using Free Format, Part 2

Most input and output functions are the same in free-format RPG IV as in fixed format, except for the location of the code within the source line

By Jim Martin

Editor’s Note: This article is excerpted from chapter 5 of Free-Format RPG IV: Third Edition, by Jim Martin.

Workstation I/O

To perform workstation input and output in free format, you use the same methods as in fixed format. The only difference is where you place the operation code and parameters in the free-format source statement.

Write/Read

The most common operation to a workstation device is the Exfmt (Write then read) operation. The write portion of this operation moves the data from the specified record to the buffer of the display device’s open data path. The device function manager checks the option indicators and performs the selected options, such as setting display attributes, displaying error messages, or performing keyword functions.

The read part of the Exfmt operation sends the output buffer to the device and then waits for input from the device. The input occurs when the user presses either Enter or an enabled function key. The operating system handles non-enabled function keys by returning a message informing the user that the key is not available.

Write

The Write operation usually is associated with a display file for which an overlay function is needed—for example, for a trailer record preceding a subfile control record or a message subfile record preceding a regular display format.

Read

We seldom use the Read operation in a display file. You can execute it immediately after a Write operation, but programmers usually use the Exfmt operation to perform this combination. Read is more commonly used when the specified file is an Intersystem Communications Facility (ICF) file.

ICF I/O

RPG IV supports ICF files by letting you specify device WORKSTN in the file declaration. The RPG operation codes that you specify dictate what the communications device will do. The file declaration includes a device name (Dev) keyword, which ICF requires. The value of this keyword corresponds to the device entry names in the ICF file.

An Exfmt operation to an ICF record becomes a three-function combination: send a record, send a “turnaround” instruction to the other station, and then receive a record from the other station. The Write operation is simply a send-record operation. The Read operation with a record format is a receive operation. If the Invite keyword (DDS in the ICF file) was used previously on a Write operation, a Read operation using the ICF file name becomes a read-from-invited-devices operation. In communications lingo, this means that any device in the device file (that has been invited) may now send to the program. With this kind of Read, you can specify a record wait time limit that, if reached, can cause control to return to the program along with a time-out exception.

Dsply

The Dsply operation is available in free format to provide the same functionality as its fixed-format counterpart. Because this operation comes from an original RPG format, you must remember to code the operation Dsply first, followed by Factor 1 information and then Factor 2 information.

Listing 5-6 shows examples of workstation I/O using free-format RPG IV.

Listing 5-6: Workstation I/O operations available in free format

Printer Output

In free-format RPG IV, you code printer output, whether program-described or externally described, the same way you do in fixed format.

Overflow Indicator

The overflow indicator has been with RPG for a long time. Indicators OA–OG and OV have served us well. In RPG IV, an externally described printer file can use any numeric indicator. As of V5R1, you can also use a named indicator.

This feature can make RPG IV programs that use printer files easier to read and maintain. The named or numbered indicator is automatically set to *On when printing occurs on or after the overflow line specified in the printer file definition. You can change the overflow line permanently by using the CHGPRTF (Change Printer File) CL command, or you can change it temporarily by using the OVRPRTF (Override with Printer File) command.

Write

The Write operation uses a record name defined in the printer file and causes all output for the record to be printed.

Except

You can use the Except operation with program-described printer files to print using output specifications. Program-described printing provides nearly all the functionality of externally described printing.

Listing 5-7 shows examples of printer output using free-format RPG IV.

Listing 5-7: Output operations in free format

More of Jim’s Free-Format RPG IV is coming soon in an upcoming issue of MC RPG Developer. Can’t wait?  You can pick up Jim Martin’s book, Free-Format RPG IV: Third Edition at the MC Press Bookstore Today!

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Jim Martin holds a BS degree in mathematics and an MS in computer science. For 26 years, he was employed by IBM, where he wrote RPG applications for customers and worked in the programming laboratory as a programmer on portions of CPF and the OS/400 operating system. After leaving IBM, Jim took post-graduate work in computer science and performed RPG training. He is an IBM-certified RPG IV developer and author of multiple bestselling editions of Free-Format RPG IV, which, since the book’s initial publication in 2005, have taught thousands of RPG IV programmers how to be successful with the free-format coding style.

MC Press books written by Jim Martin available now on the MC Press Bookstore.

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