Dealing with Overflow of Fragmented Packets

Most of my information written in this blog can be found at NFS for clusters and Optimizing NFS Performance

One method to check for fragmented packets issues with the NFS Server is to use the IP: ReasmFails in the file /proc/net/snmp

# head -2 /proc/net/snmp | cut -d' ' -f17

ReasmFails represents the number of fragment reassembly failures, if the ReasmFails goes up too quickly during heavy file activity, it means that the system may be having issues

According to Optimising NFS Performance, if the network topology is too complex,  fragment routes may differ, and may not all arrive at the Server for reassembly.  Once the number of unprocessed, fragmented packets reaches the number specified by ipfrag_high_thresh (in bytes), the NFS Server kernel will simply start throwing away fragmented packets until the number of incomplete packets reaches the number specified by ipfrag_low_thresh.

You can reduce the number of lost packets on the server by increasing the buffer size for fragmented packets.

$ echo 524288 > /proc/sys/net/ipv4/ipfrag_low_thresh
$ echo 524288 > /proc/sys/net/ipv4/ipfrag_high_thresh

which is doubling the defaults

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