First post, by Disruptor
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- Oldbie
In 2020 I've introduced a test with the Adaptec AIC-3860Q SCSI bridge that is found on some controllers like the 2940U2W, 19160, 29160.
Extending a SCSI bus with Adaptec AIC-3860Q (2940U2W and more)
Now I have got 9 controllers with that bridge chip in my portfolio, and enough cables of course.
What to do with that?
Install them in 2 computers. Make a bridge. And a path. And another bridge. How far can I go?
Left of the bridges there was an LSI U320 controller which had connected a ST336607LW drive.
Right of the bridges there was a LSI 875 based controller.
In the middle I used one 19160, 2 29160, and 6 29420U2W.
Each of the controllers got an own SCSI ID.
All controllers with bridge chip were configured to disable BIOS and to disable SCSI reset.
I used a interleave configuration of LVD-SE-LVD-SE...
Then I have benchmarked the SpeedSys Buffered Read speed in these configurations:
Bridges Narrow Wide
9 12350 kB/s ---
8 13557 kB/s 26190 kB/s
7 14964 kB/s 28852 kB/s
6 16518 kB/s 31641 kB/s
5 18309 kB/s 35018 kB/s
4 18319 kB/s 35047 kB/s
3 18329 kB/s 35086 kB/s
2 18339 kB/s 35123 kB/s
1 18349 kB/s 35157 kB/s
0 18359 kB/s 35194 kB/s
Conclusion: In reasonable usage, it doesn't matter whether you have a bridge or not in your SCSI bus, when you look at the performance.
Another of my tests was whether a narrow connection over LVD was possible.
Well, it was, but just up to 40 MB/s. Connecting a 19160 and a 29160 together via LVD and disabling wide negotiation results in a drop from 160 to 40 in the speed box of Adaptecs SCSISelect utility. Perhaps narrow differential cables aren't specified for that speeds...