Hello! Last night I was trying to get KDE5 to start up on my new machine, and a couple of KDE's processes kept crashing, dumping cores like the one below: -rw-------? 1 mi??? wheel? 45780992 Jul 23 22:28 ksplashqml.core After, maybe, 10 such rounds -- each generating two core-dump -- ZFS hung... The machine was otherwise responsive, but any attempts to access the ZFS filesystems would hang as NFS would, when the remote server stops responding... Pressing Ctrl-T would show the process in the state named "zfs". According to "systat -vm", all four disks involved in the raidz1 were writing in excess of 100MB/s, so I let it be for a few minutes, but nothing improved -- and the writes continued... I pressed Ctrl-Alt-Del, which initiated a shutdown, but the shutdown hung as well ("some processes would not die") and I had to do a power cycle... The sole zpool consists of 4 3TB drives and a 16GB log (on an SSD) thus: ??????? NAME??????? STATE???? READ WRITE CKSUM ??????? aldan?????? ONLINE?????? 0???? 0???? 0 ????????? raidz1-0? ONLINE?????? 0???? 0???? 0 ??????????? da0???? ONLINE?????? 0???? 0???? 0 ??????????? ada1??? ONLINE?????? 0???? 0???? 0 ??????????? da2???? ONLINE?????? 0???? 0???? 0 ??????????? da1???? ONLINE?????? 0???? 0???? 0 ??????? logs ????????? ada0e???? ONLINE?????? 0???? 0???? 0 It reports no data-errors after reboot. There are multiple filesystems on it, among them /home. The box is running a very recent FreeBSD-11/amd64 (r336626). It has 4 Xeon cores and 128GB of RAM. The pool was created under FreeBSD-10 -- after this incident I upgraded it. What happened? Thanks! Yours, -mi