Friday, March 28, 2008

WAN war breaks out over changed file formats in AutoCAD MEP

Article sent to me from a user. Thanks for the link. I summed up the article below. From the article, it sounds like Autodesk doesn't have a solution yet. I don't know much about the various WAN acceleration applications, but I thought I'd share these articles with you.

It seemed like a good idea at the time...
Bryan Betts, Techworld

A changed file format has sparked off a fierce war of words between users, WAN acceleration vendors and Autodesk, which significantly changed its DWG drawing file format in both the last two versions of AutoCAD.

The result, is that WAN optimisation gear from the likes of Riverbed Networks - which has a strong user-base in CAD - is no longer able to accelerate file transfers over the WAN. Given that many CAD-using companies need to share drawings across multiple offices, that's a big problem.

At issue is a new dynamic file format which deliberately makes a saved file look completely new, even if it is only an edited version of an existing file, says Riverbed VP Alan Saldich. That means block-level caching schemes can't do what they'd normally do, which is to send only the changes over the WAN.

Format errors

"To improve the speed of the application itself, they changed the file format so that every time you change the file, every bit gets scrambled," Saldich explains. "If you FTP the file twice or reopen it without saving, we can work on that.

"There's only two ways to solve it. One is for Autodesk to revert to the former file format, which seems unlikely. The other thing is they could tell us enough about the file format to undo it." Saldich explains.

In the meantime, Saldich and Autodesk VP Guri Stark have issued a joint statement advising affected users to do one of two things: either revert to an earlier AutoCAD DWG file format; or adjust an AutoCAD setting called Incremental Save Percentage (ISP) to 50, which reduces the amount of data scrambling when a file is saved.

Other WAN acceleration companies have used the issue to bash companies such as Riverbed for developing application-specific optimisation modules. However, Saldich claims it's nothing to do with those - he says they're just protocol optimisations to reduce the number of round trips, and they don't deal with file formats.

He argues that it's one of the first symptoms of a bigger problem that is only just emerging now.
"It affects any product that relies on data de-duplication, including backup and replication," he says. "I truly think the AutoCAD team were unaware of this when they did the development work back in 2004, as data de-duplication wasn't common then.

"The bigger story here is that de-duplication is a widely-used technology now, and software developers need to take account of that. We are 100 percent certain of the problem, and any vendor has the same issue, which is that you don't get to look at the data before it gets written to disk."

Aaron claims Autodesk had its own reasons for formally testing his company's gear - it is a Silver Peak user, with some three dozen of its WAN optimisers around its organisation.

Aaron acknowledges though that when Saldich argues that application developers need to be better aware of how their software will run over a WAN, he has a good point.

"The more the software developers do to address this, the more we all benefit," he says.
We asked Autodesk for its comments, but nearly two weeks later the company had still not found a spokesperson or offered any feedback.

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