Most of Ukko cluster became unavailable, apparently due to a newly intruduced bug in the Linux kernel causing the chassis switches to jam.

/cs/ukko filesystem mount did not work properly during some time.

Update 17:50

The problem was caused by a combination of broadcom network NICs and Dell PowerConnect switches.  We have now disabled flow control from cluster nodes (in old kernels it was never turned on), which hopefully stops this from happening again.