Feature

HDS reinvents high-end arrays

Ezine

This article can also be found in the Premium Editorial Download "Storage magazine: A look inside Hitachi's TagmaStor high-end arrays."

Download it now to read this article plus other related content.

Replication enables tiering
By pooling different storage resources, USP's virtualization capabilities will help make effective use of older and lower performing storage in a tiered storage structure. Tiering the pooled storage will make it possible to implement data lifecycle management, and enhance regulatory compliance efforts. With support for a variety of open systems and mainframe operating systems, it would be possible, for instance, to give mainframe computers access to lower cost SATA arrays.

United's Pilafas is paying particular attention to TagmaStore's virtualization and replication functionality to enhance his company's storage tiering. "Information lifecycle management is something we need and would like to do," says Pilafas. "It's something we'd like to do based on the capabilities of the new box."

The key to data movement in the USP virtualization architecture is HDS' new Universal Replication Engine, which will be in place with the rollout of additional software components, planned for December of this year. This will provide a single replication application that works with the USP system and across all connected storage. Data can be moved internally within a USP box, from a USP system's internal storage to an external storage device or among external devices. And again, because replication is controlled at the USP level, there's a single interface to manage data movement among

Requires Free Membership to View

disparate devices.

According to HDS, the replication engine offloads the burden of typically resource-intensive asynchronous replication to lessen the impact on hosts and network resources. HDS cites some specific techniques they employ for reducing the performance hit.

Replication services on the USP systems are journal- based. The journal resides on disk, rather than in cache, using a two-level striped architecture that HDS says will provide performance that's nearly as fast as cache. The journal helps avoid overtaxing primary storage and other network components and provides assurance that updates will be properly handled. For example, if bandwidth is exceeded during the replication process, the updates will continue to be written to the journal until enough bandwidth is once again available. HDS claims that with the journaling method, the replication engine can withstand long link outages, and it's more effective than the more common approach of using a bitmap to keep a record of the data tracks that need to be updated.

Most replication products use a "push" technology, which puts the burden of the replication process on the primary array. The Universal Replicator Engine, like IBM's XRC, uses pull technology to offload that burden. With the journal residing on the primary array and reader tasks on the secondary storage handling the changed data, performance degradation on the primary is substantially reduced. Bandwidth, too, is conserved. Typically, bandwidth for replication is allocated based on peak I/O activity. But because the journal will absorb the peaks, HDS suggests that required bandwidth can be reduced by as much as half.

The same journaling process can help diminish geographic issues for long-distance replication from one USP box to another, which would make it effective for disaster recovery. Using USP systems at separate sites makes it possible to provide disaster recovery for multiple data centers.

This was first published in September 2004

There are Comments. Add yours.

 
TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to: