| Title: | FDDI - The Next Generation |
| Moderator: | NETCAD::STEFANI |
| Created: | Thu Apr 27 1989 |
| Last Modified: | Thu Jun 05 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 2259 |
| Total number of notes: | 8590 |
Hi,
This might be a very simple question. A VAX 7610 can support up to 4
XMI bus (100 Mbytes/sec); each XMI has 12 slots. A DEC FDDIcontroller
400 can be installed in one of these 12 slots.
Is it reasonable to say that if the same XMI adapter is shared by
tapes, disks, etc., the throughput of the FDDI controller might not
reach 100 Mbit/second? My customer is going to install a FDDIcontroller
and would like to know whether adding a dedicated XMI adapter for the
controller is necessary.
BTW, is there any formal document specifying this throughput achieved
by DEMFA (FDDIcontroller 400)?
Any input will be greatly appreciated.
Thanks and Regards,
Fung Siong
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 979.1 | XMI is much faster than DEMFA | WONDER::WILLARD | Mon Aug 30 1993 18:06 | 22 | |
Pardon the tardy response - I don't read this notesfile often. The XMI is good for ~100 MByte/s, the DEMFA is ~12 MByte/s, and all other XMI I/O widgets are slower than the DEMFA. You can put several I/O widgets on the XMI with concurrent activity with no noticeable impact on the DEMFA's performance, because the DEMFA has some overlap and buffering on DMA and because the XMI is pended and works correctly even when saturated. For a crude approximation assume each DEMFA or DWMBB is a 12 MB/s load, each CIXCD is a 8 MB/s load, each DWMVA or KCM44 or KDM70 or KFMSA is a 6 MB/s load, and each DEMNA is a 1 MB/s load. If the total load is <50 MB/s, you are pretty safe; else, you may want to consider more details (performance differences due to transfer sizes and transfer directions and huge performance differences due to the workload not being able to use I/O widgets to rated capacity), or you may simply decide to buy another XMI to reduce the risk. Of course, there is no guarantee that your workload will achieve 100 Mbit/s via the DEMFA, regardless of other XMI loads. Cheers, Bob | |||||
| 979.2 | KONING::KONING | Paul Koning, A-13683 | Tue Aug 31 1993 13:09 | 6 | |
The preceding doesn't take into account descriptor access overhead. For large packets you should have plenty of margin, but for minimum size packets you will have very little. If you want good performance, always use the biggest packet size you can. paul | |||||