* David Leach: > I've been looking at AoE and I'm trying to understand what affect the > Ethernet CRC-32 data integrity checking has on the AoE communications?
The Frame Check Sequence follows the payload and AFAIK it covers the whole frame. I have found claims that the CRC-32 algorithm would loose its effectiveness with frames longer than 12000 bytes. > Particularly when going to GbE and jumbo frames support there seems to > be some data out there that there is a chance that the CRC32 won't > detect the error in the frame and with a protocol like AoE that error > would most probably end up being written to the target disk. I am sure that there is some theoretical foundation to that 12kByte limit, along with assumptions about the expected rate of bit errors. > Has anyone done any analysis or have any response to AoE's ultimate > reliability for missed error detection of bad frames? > > I think that there is a further problem to understand and that is with > network connection points. AoE is not routable but that doesn't mean > you can't use network switches to interconnect initiators with their > AoE targets and at these switches there seems to be a possible error > point introduced which AoE isn't protecting against? Are there best > practices for AoE installations to protect against these error points? I have run into problems with cheap switches that have led me to similar concerns: In my setup, a Linux box exports several targets to .1q tagged VLANs over a single physical interface. The initiator interfaces use "plain" Ethernet (no VLAN tags), so the switch has to discard the tags and regenerate the FCS. Nowadays, I use HP 2810 switches and to my knowledge everything is fine, but much time was wasted before with cheaper hardware that would hang/reboot under high load and apparently barf over the data in the process while still managing to get the CRC-32 bit right. Perhaps an extension to the AoE protocol that implements a checksum for the Ethernet payload might be useful to detect such errors. Cheers, -Hilko ------------------------------------------------------------------------------ The Next 800 Companies to Lead America's Growth: New Video Whitepaper David G. Thomson, author of the best-selling book "Blueprint to a Billion" shares his insights and actions to help propel your business during the next growth cycle. Listen Now! http://p.sf.net/sfu/SAP-dev2dev _______________________________________________ Aoetools-discuss mailing list Aoetools-discuss@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/aoetools-discuss
