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From: Kai Gallasch <gallasch@free.de>
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Subject: FreeBSD 9.1 and swap on zfs
Date: Mon, 8 Apr 2013 15:08:55 +0200
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Hi.

When running a ZFS on root FreeBSD install..

is it for FreeBSD 9.1 (ZFS v28) still not advisable to use a vdev as =
swapspace? - like:

# zfs create -V 8G \
	-o org.freebsd:swap=3Don \
	-o sync=3Ddisabled \
	-o primarycache=3Dnone \
        -o secondarycache=3Dnone rpool/swap

# swapon /dev/zvol/rpool/swap

Often voiced fears for swapping on zfs are, that at the moment the =
server starts to swap, ZFS will start to compete for memory with the =
short-on-memory server itself (reason for swapping) and the system will =
lock up shortly after.

Seems a lot of ZFS-on-root single disk setups make use of an extra swap =
partition on the root-disk.

People booting of a mirrored-zpool often seem to have a swap partition =
on both disks forming the zpool and use those as devices for a gmirror. =
They then use the gmirror device as swap.

Which approach is the recommended one?
Swapping to ZFS *or* a swap partition / gmirror on top of two =
partitions?=20

Regards,
Kai Gallasch.