IBM eServer zSeries 900 Technical Guide

Chapter 5. Sysplex functions 191

– The PPRC configuration must have one-to-one correspondence between each primary

SSID and secondary SSID.

– Hyperswap devices cannot attach to systems outside the Parallel Sysplex.

򐂰 Production systems must have sufficient channel bandwidth to primary and secondary

PPRC disk subsystems. Because of bandwidth considerations, it is recommended to use

FICON for zSeries to disk attachment if the distance between sites exceeds 5 kilometers.

5.4.2 GDPS/XRC

GDPS/XRC is a combined hardware and software asynchronous remote copy solution. The

application I/O is signalled completed when the data update to the primary storage is

completed. A DFSMS component, called System Data Mover (SDM), asynchronously

offloads data from the primary storage subsystem’s cache and updates the secondary disk

volumes in the recovery site.

The physical topology of a GDPS/XRC (see Figure 5-7 on page 192) consists of a base or

Parallel Sysplex cluster in the application site (site A). The recovery site (site B) can be

located virtually at any distance from site A. In this example, XCR System Data Mover will be

executing in site B, but it can be located in other sites, depending on the installation’s

requirements.

All critical data resides on storage subsystems in site A (the primary copy of data) and is

mirrored to site B (the secondary copy of data) via XRC asynchronous remote copy.

There is new peer-to-peer Virtual Tape Server (VTS) support for a GDPS/XRC configuration.

Peer-to-peer (PtP) VTS support was initially announced for a GDPS/PPRC configuration in

November 2001. PtP VTS support has now been extended to a GDPS/XRC configuration.

The PtP VTS provides a hardware-based duplex tape solution and GDPS is designed to

automatically manage the duplexed tapes in the event of a site failure. By extending GDPS

support to data resident on tape, the GDPS solution is designed to provide continuous

availability and near transparent business continuity benefits for both disk- and tape-resident

data. Enterprises should no longer be forced to develop and utilize processes that create

duplex tapes and maintain the tape copies in alternate sites.

GDPS/XRC provides the following benefits:

򐂰 Disaster recovery

򐂰 RTO between one and two hours

򐂰 RPO less than two minutes

򐂰 Protects against metropolitan as well as regional disasters (distance between sites is

unlimited)

򐂰 Minimal remote copy performance impact

GDPS/XRC hardware requirements

In addition to the GDPS/PPRC hardware prerequisites, XRC with ESS also requires the

following:

򐂰 For the Primary ESSs, the XRC feature must be enabled. Support is provided by

XRC-capable Licensed Internal Code.

򐂰 If primary volumes are shared by systems running on different CPCs, a Sysplex Timer

(IBM 9037 Model 2) is required to provide a common time reference.