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Updating the PowerScale cluster setting of net.inet.tcp.reass.maxqueulen to 2048 resolves these performance problems. This change is unnecessary for macOS 11+ users. The procedure for making the change is outlined in the following Dell KB article (login required): Sysctl Security Change Can Affect TCP Performance On Degraded Networks OneFS v8.1.0+.
Increasing net.inet.tcp.reass.maxqueulen can make the PowerScale cluster more vulnerable to certain DOS attacks, but if the PowerScale cluster is on a secure, private network, the risk is minimal.
To view the current setting of net.inet.tcp.reass.maxqueuelen, run the following CLI command (default value is 100) from OneFS:
sysctl net.inet.tcp.reass.maxqueuelen
Temporarily change the value on a particular PowerScale node:
sysctl net.inet.tcp.reass.maxqueuelen=2048
Have the clients check the network to confirm that the performance issue has been resolved. The change should be immediate: the macOS clients do not need to unmount/remount the volume.
If the issue is resolved, change the value for the whole cluster on reboot by editing the following file:
/etc/mcp/defaults/sysctl.conf
If the sysctl exists, edit that line. If it is not in the file, add these lines to the bottom of the file:
net.inet.tcp.reass.maxqueuelen=2048
Push the change to all nodes in the cluster:
isi_sysctl_cluster net.inet.tcp.reass.maxqueuelen=2048