Although smart switching is a long way from being taken up by customers, the move does maintain Cisco’s momentum and technical credentials in an area where it is at the front of the pack.

The demo at Storage Networking World in Phoenix, Arizona next week will involve software from Alactritus, Kashya, and Topio, whose applications would otherwise run on in-band servers or appliances located within a SAN.

Using what Cisco has dubbed its Data Tap protocol, the appliances will still be used to host the applications. But some of the workload will be handed off to the MDS 9000, in a way that Cisco says will eliminate the traditional drawbacks of using in-band appliances.

Cisco was adamant about giving absolutely no indication of when any Data Tap technology will ship, or whether it is working with any software suppliers other than the start-up trio.

The MDS 9000 is currently sold only via third-party OEMs including HP, IBM, EMC and Hitachi. Asked whether those four giants would be interested in qualifying and reselling software from start-ups, Cisco’s senior product manager Rajeev Bhardwaj said: At this time we have to figure that out. We’re in discussion with our partners. Data Tap is an incremental facility for the MDS 9000.

Data Tap is a different form of smart switching to what Cisco has already shipped. It does not involve porting a storage application from an in-band appliance onto the MDS 9000 in order to – among other things – eliminate the two major drawbacks of in-band appliances, which are that they present a potential bottleneck on data throughput, and a single point of failure.

Instead, Data Tap allows the MDS 9000 to take on only some of the work that the appliance would otherwise do, but does keeps the appliance out of the way so that it cannot be a bottleneck, and if it fails cannot be a discontinuity in the network that prevents servers from talking to disk or tape devices.

In the Data Tap architecture, the appliance is attached to the MDS switch, not directly in the data path, but to the side of the network. The appliance still needs to have access to data traffic to do its work.

For example Alacritus’ software keeps a log of write commands sent from servers to disks to provide continuous data protection against software screw ups. If there is a problem, Alacritus’ application uses this log to turn back the clock and recreate data as it was before the software error occurred.

When running standalone without the MDS 9000, an Alactritus appliance has to filter all data traffic, and make a copy of all write commands related to the applications it is protecting. This can slow throughput.

When connected to the MDS 9000 via Data Tap, the MDS and its fast port-level processors instead do that filtering. Any I/O commands that servers send always go to disk. A copy goes to the appliance, but the appliance does not own [control] the data traffic. We’re preserving the integrity of the I/O between server and disk, said Bhardwaj. Hence the name Data Tap.

DataTap will not suit all storage applications, Bhardwaj said. For example it would not suit virtualization applications that redirect data traffic by re-mapping I/Os, and so must work on the original I/O requests themselves, and not just a copy.

This article is based on material originally published by ComputerWire