Wednesday, April 23, 2008

WAN problems with DWG 2007 / Problèmes de WAN avec DWG 2007

Here is an article from the April 2008 issue of Cadalyst Magazine. It seems to confirm what a few clients of brought to my attention in the last few months.

Voici un article provenant de la revue Cadalyst du mois d'avril 2008. Ca semble confirmer ce que quelques clients on porter à mon attention dans les derniers mois.


DWG 2007 Format Found to Choke WAN

Ray Sirois, IT director for the New England–based engineering firm Wright-Pierce, is putting the brakes on his company's migration to AutoCAD 2008 "due to poor performance issues" related to the use of wide-area network (WAN) accelerators such as RiverbedTechnology Steelhead appliances. Wright-Pierce attributes the performance degradation to "AutoCAD's version 2008 Save command reorganizing or reordering much of the content within the DWG file."

"We suspected the problem actually existed to a lesser degree in version 2007," Sirois noted. "However, in our testing, we found the problem is much worse in version 2008." In addition to putting a strain on WAN transfer, the change can have a negative effect on IT backup operations. "Our Exagrid disk-to-disk backup system heavily leverages data de-duplication to enable months of backups to be stored on one disk array," Sirois said. "If all our DWG files look to be 80–90% new data each time they are touched, then that kills the effectiveness of the backup system."

Ironically, the modified DWG 2007 format was meant "to make it more compact and improve performance for AutoCAD users." Nevertheless, Autodesk acknowledges that "one of the side effects of the DWG format changes is that when users perform a complete save from within AutoCAD (as opposed to an incremental save), virtually every byte of the file gets changed — even if zero changes were made to the file itself" (see "Potential for reduced write performance for Riverbed WAN links when working with AutoCAD 2007 DWG files" at the online AutoCAD Services and Support page, published March 12, 2008).

The affected products include AutoCAD 2008 and 2007, AutoCAD Architecture 2008, Autodesk Architectural Desktop 2007, and AutoCAD Civil 3D 2008 and 2007. While it tries to come up with a permanent fix, Autodesk proposes the following workarounds:

  • Use a feature in AutoCAD called Incremental Save Percentage (ISP) and set it to 50.
  • Use a version of the DWG format other than the AutoCAD 2007 DWG format.

Wright-Pierce is cautiously experimenting with the first approach. Sirois hopes rumors of increased potential for file corruption with higher ISP settings will prove unfounded. For his firm, "saving the file in an earlier version's format is certainly not a workaround at all for Civil 3D and may not be for other verticals such as AutoCAD Architecture," he observed. "The newer model objects and entity types created in Civil 3D are simply not supported in earlier versions. Such objects can't exist in earlier-version DWG files without losing all their intelligence."

Sirois is encouraged by Autodesk and Riverbed's reaction. "The big news is, Autodesk has become enlightened about how important multioffice interoperability is to its mid-size and large customers," he noted.

Silver Peak, Riverbed's competitor, jumped at the opportunity to declare, "There has been uproar recently among AutoCAD customers because certain older WAN optimization products appear incompatible with newer AutoCAD file formats. Silver Peak has worked with Autodesk and other customers to verify that Silver Peak's NX appliances do not suffer this limitation."

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