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List:       freebsd-fs
Subject:    zfs - reboot after panic
From:       Kiriakos Georgiou <zebekias () gmail ! com>
Date:       2016-01-24 20:51:24
Message-ID: A4C07583-2AB4-436C-B5BE-34C952C3419B () gmail ! com
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Hello,

I've been happily running a FreeBSD 10.1 fileserver (updated regularly via \
freebsd-update) with ZFS zvols served out via iscsi.  Total RAM is 8G. For 2-3 months \
I regularly successfully run some heavy duty checksuming via unison (it's kind of \
like rsync, but does bidirectional syncing).  I recently updated the OS to \
10.1-RELEASE-p26, and soon after I started to consistently get kernel panics when I \
run unison to sync certain files across my VMs:

reboot after panic: I/O to pool 'zdata' appears to be hung on vdev guid ....

First I thought a bug must have been introduced, but after some googling I set my \
vfs.zfs.arc_max to 4G (50% of my ram) and hammered zfs via a massive unison sync.  I \
monitored memory via top.  ARC grew quickly to 4096M and stayed there.  Free memory \
would slowly drop all the way to just under 1G but then it'd suddenly jump to over \
2G, then slowly go down to 1G and jump to 2G again so on.  I suspect it was a RAM \
starvation issue that is now resolved by tuning the ARC max.  I've no idea why it \
started happening.  I just wanted to share it with you.  Does the "fix" make sense?

Thanks,
Kiriakos
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