The upgrades fill in what IBM admits were functional deficiencies in its FlashCopy snapshotting utility, and allow its Peer to Peer Remote Copy software to offer multi-hop or cascaded mirroring out-of-the-box.

The cascaded mirroring in PPRC version 2.0 allows companies to mitigate the problem that very long distance data mirrors cannot operate synchronously without affecting application performance. Over large distances the time taken for electrical or optical signals to complete round-trip journeys results in the source application being slowed by having to wait for the distant mirror to acknowledge that it has received each copy of a transaction. The alternative is to create a mirror which operates asynchronously, and so does not slow performance – but because of the time lag also does not offer the same level of protection against a failure at the primary site.

A compromise is to mirror synchronously to a relatively local site, and mirror again from there asynchronously to a distant site, for example from Wall Street in New York to neighboring New Jersey synchronously, and New Jersey to California asynchronously. If the same tornado takes out both New York City and New Jersey, at least there’s an asynchronous mirror in California.

The new version of PPRC allows this to be done without having to use intermediate snapshotting software, or write any custom scripts, as was required previously. IBM said that although EMC’s mirroring software can be used to provide multi-hop mirroring, it requires customers to also license EMC’s snapshotting software.

EMC responded by telling ComputerWire that IBM advises its customers that plan to create cascaded mirrors using PPRC 2.0 to also license the IBM snapshotting software in order to create a safe copyof data at the remote site.

IBM said that until now it has emphasized the performance of its FlashCopy software to potential buyers, who may have been put off from buying the Shark by greater functionality in the utilities offered for rival hardware such as EMC Corp’s Symmetrix disk array. Now it performs excellently and has these key functions, the company said yesterday.

FlashCopy 2.0 replaces version 1.0 of the software and on the latest series 800 Sharks reduces by a factor of ten the time taken to quiesce data before data is copied to a snapshot. Other improvements include the ability when attached to z/OS mainframes to copy individual datasets rather than entire LUNs or groups of data volumes, and to make incremental snapshots – ie to synchronize previous snapshots with source data.

Source: Computerwire