ping/ssh/ftp Does Not Work As Expected With 2G/4G Qlogic FC HBAs Using FCIP With MTU=9000 (Doc ID 2108793.1)

Last updated on OCTOBER 05, 2022

Applies to:

Symptoms

The fcip implementation of the currently released qlc driver, rev 4.03 or older, does not work as expected. First, the "ping -s <ip>" does not work if the data payload is one byte above the configured Maximum Transmission Unit (MTU) setting.. For example if the MTU size is set to 9000, then running this command will fail:

Note, the total transfer count (from the above FC frames) is our 8973 bytes. The echo code 0 and code 9 seem to be legal from a Fibre Channel perspective. The problem is if the echo code 9 frame is sent "out of sequence", then the receiving end does not know how to handle such condition (mainly the IPS2300 HBA), and it does not echo back the received data. If we get frame sequence 0, 1, 2, 3, 4 of code 0, followed by the echo code 9 frame, then it works.

For the case where the ping is initiated from the ISP2300 HBA (which sends the frames in sequence), the ISP2400 HBA receives that data correctly (i.e., in sequence), but when the ISP2400 HBA echos the data back to the ISP2300 HBA, the ISP2300 HBA does not know how to handle the out of sequence frames, and the ping hangs/fails..

The second symptoms seen in the currently released qlc driver rev is the performance. For example, the performance of ftp get's is in Kbytes/sec where as the performance of ftp put's are in MBytes/sec.

Changes

Starting with the 4Gb/sec Qlogic HBAs, which utilize a Fibre Channel ASIC (IC) that implements multiple DMA channels, and allows the QLC driver to start multiple simultaneous transfers on these DMA channels. This approach worked well when the requests are issued to Direct-Access Storage Devices (DASD). On the other hand, this approach does not work very well when used in fcip configurations. So, if These Multi-DMA-Channels HBAs are connected to 2Gb HBAs (which implements a single channel DMA), through a direct connect or a Fibre Channel switch (testing was done on both Brocade and qlogic FC swithes), then the pings will hang and fail. 

Cause

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