Hit another mdadm "hanger" today. No more reading possible and md4_raid6 stuck at 100% CPU. I've now moved the write journal off the RAID1 device. So it's not a "nested" RAID any more. Hope this will help. With only one hardware device used as write cache, I suppose only write-through mode[1] is suggested now. 1: https://www.kernel.org/doc/Documentation/md/raid5-cache.txt > On Feb 11, 2021, at 11:14, Manuel Riel <manu@xxxxxxxxxxxxx> wrote: > > I'm also hitting the exact same problem with XFS on RAID6 using a RAID1 > write journal on two NVMes. CentOS 8, 4.18.0-240.10.1.el8_3.x86_64. > > Symptoms: > > - high CPU usage of md4_raid6 process > - IO wait goes up > - IO on that file system locks up for tens of minutes and the kernel reports: > > [Wed Feb 10 23:23:05 2021] INFO: task md4_reclaim:1070 blocked for more than 20 seconds. > [Wed Feb 10 23:23:05 2021] Not tainted 4.18.0-240.10.1.el8_3.x86_64 #1 > [Wed Feb 10 23:23:05 2021] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [Wed Feb 10 23:23:05 2021] md4_reclaim D 0 1070 2 0x80004000 > > Already confirmed it's not a timeout mismatch. No drive errors reported. SCT Error Recovery > Control is set to 7 seconds
