Flaws in Via chipsets hit ATA/133, SCSI performance

A serious design defect in Via chipsets results in boards based on them substantially underforming motherboards with chipsets from Intel, SiS and ALi, a series of tests conducted by tecChannel.de has shown. The problem affects boards using both Intel and AMD chips, and the hit to hard disk performance is sufficient for tecChannel to say: "we can currently not recommend VIA chipsets for professional users who demand high performance from their hard drives and think about setting up RAID configurations."

The problem is that Via chipsets are currently unable to take full advantage of the performance of PCI. Controller cards with Ultra-ATA/ 133 chips have a maximum theoretical throughput of 133Mbytes/s (or 127.2 in real megs), and tests of non-Via motherboards with Promise and Highpoint controllers (using either Maxtor D540X or D740X) showed burst mode transfer speeds of 95-117Mbytes/s. The same tests performed on a variety of Via boards came up with speeds of 63-78Mbytes/s, clearly indicating that there's something unpleasant going on here.

Forther investigation provided an explanation. According to tecChannel: "Normally, a burst should be performed continuously and without any interruption... The length of a burst, however, can differ depending on the data transferred.

"With VIA boards, this high speed transfer from the cache of a hard drive is constantly interrupted within a couple of µs. It has then to be re-initiated... Therefore, the effective burst rate drops to 64 to 90 MBytes/s at best... In contrast to chipsets from Intel, SiS and ALi VIA's products seem to have difficulties with maintaining high transfer rates close to the maximum speed of PCI for a longer time. As with ATA/133 PCI has a theoretical maximum bandwidth of 127,2. It seems fair to conclude that VIAs implementation of a PCI bus must be the reason for the problems found."

Via also underperforms when it comes to SCSI. Systems set up with Intel 845 and Via P4X266A, plus an Adaptec RAID-2100S, showed performance around 30 per cent better for the Intel system. Longer bursts used by the Intel system result in much better performance. So if you buy a high performance controller then put it in a board via a Via chipset, right now you're probably wasting your money.

According to tecChannel Via has confirmed the problem, and says it is working on a solution. However it is not clear whether new drivers will be enough, or whether it will need a redesign of the chipsets. There is an unofficial patch produced by George Breese of Networking Resources available here, but as tecChannel says, you use this at your own risk.

The full, highly detailed report can be read here. ®