On 06/14/2007 03:51 PM, Tom Buskey wrote: > On 6/14/07, *Flaherty, Patrick* <[EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>> wrote: > > I'm not the best with these bit/byte problems so I might be wrong, > but..... > > A PCI bus can pass 1056 bits a second (32 bit, 33 mhz) > tcp/ip over head is somewhere around %20 (1056 * .8 = 844.8) > BTW, that's a standard PCI bus. Usual performance after taking out PCI overhead is a bit over 500Mbit (see the 50MB rate below). PCI-64 bit and PCI-66Mhz/100Mhz multiply those rates as standard PCI is 32bit/33Mhz, so a PCI-64bit can handle twice the bandwidth of PCI-32bit and PCI-66Mhz/64bit can handle 4 times. You're now easily in the Ghz range, even if you have other devices on the bus.
I haven't checked to see what PCI-X/PCI-E does, but I've hit pretty high speeds with it (see below). > > > What can you reasonably expect a pci gigabit card to give you for > through put? > > > The author of O'Reilly "Unix Backup & Restore" says you should expect > a maximum throughput around 50MB/s for backups over gigabit. 500Mbit is the untuned rate I saw under Linux using netpipe. With a bit of kernel tuning I could get to the 825-875Mbit range. > > > PCI Buses are generally shared (save high end server boards) right? > > > Yep. Higher end systems will have multiple PCI buses. The Sun v890 > has 4 seperate buses and you can distribute the cards based on Most server-class systems have multiple busses or at least have a separate bus for its Ethernet controllers. Even on a desktop-class system, there's not a whole lot else going over that PCI bus unless you have a second Gig Ethernet card or a SCSI card. > > > On top of that, if hdparm says timed disk writes are around 40MB, what > could you see for sustained download speeds? Maybe a static cached > webpage could saturate a gig connection, sustained 5 gig http download > couldn't right? > > Anyone have real world answers for that stuff? > > > What if you're downloading to RAM disk? > When I've been doing my network measurements I've been going from > /dev/zero to /dev/null to eliminate the storage speed effects. The reason we did the timing was a few: - MPI/PVM is usually CPU-CPU (no disk) and we don't want to spend the additional money for a high speed interconnect, so making the Ethernet connection really fast was a 0-cost improvement. - The faster you can shuttle data to a device, the less time that device (and others trying to contend for bandwidth) are waiting. -Mark _______________________________________________ gnhlug-discuss mailing list gnhlug-discuss@mail.gnhlug.org http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
