Date: Tue, 10 Dec 2013 16:35:31 -0700 From: John Nielsen <lists@jnielsen.net> To: Shane Ambler <FreeBSD@ShaneWare.Biz> Cc: Oscar Prieto <oscarmpp@gmail.com>, Benjamin Lutz <benjamin.lutz@biolab.ch>, "freebsd-stable@freebsd.org Stable" <freebsd-stable@freebsd.org> Subject: Re: Swap on ZFS - bad idea? (swap_pager: indefinite wait buffer) Message-ID: <197090E6-DE73-40C2-8475-E102640B0DAF@jnielsen.net> In-Reply-To: <52A78CB3.8050109@ShaneWare.Biz> References: <OFB3F5370B.79D00F5F-ONC1257C3D.0038AB15-C1257C3D.003AB574@biotronik.com> <CAK9wqRrug7G5w3HyT7WiLitS8LJ-E1vYUNsD0X0EjkYfxcqgoQ@mail.gmail.com> <52A78CB3.8050109@ShaneWare.Biz>
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On Dec 10, 2013, at 2:50 PM, Shane Ambler <FreeBSD@ShaneWare.Biz> wrote:
> On 11/12/2013 04:06, Oscar Prieto wrote:
>> Personally I still have to read an announcement telling that swap on zfs is
>> relliable. I'm still using a dedicated swap partition on every install due
>> to that kind of behaviour.
>
>> On Tue, Dec 10, 2013 at 11:41 AM, Benjamin Lutz <benjamin.lutz@biolab.ch>wrote:
>>
>>> This sort of hang seems to happen every couple of months. I'd really like
>>> some pointers on how to increase the stability of this system. Maybe there
>>> are some more tunables I need to adjust? Or is swap on ZFS maybe just not
>>> a great idea?
>
> I did read somewhere that it is not recommended to use a zvol for swap.
>
> Personally I did setup swap on a zvol when I first started with zfs.
> Turning it off showed a performance boost but I never had any errors
> from it. I had only setup a single disk zpool so maybe its swap on zfs
> raidz that causes the errors.
I've never seen a problem with swap on a zvol in any currently-supported version of FreeBSD but as always, YMMV. I use the below commands to create and activate a swap volume (2G in this example):
zfs create -V 2G -o org.freebsd:swap=on -o checksum=off -o compression=off -o dedup=off -o sync=disabled -o primarycache=none ${rootzpool}/swap
echo "/dev/zvol/${rootzpool}/swap none swap sw 0 0" >> /etc/fstab
swapon -a
Most of those options are from https://wiki.freebsd.org/RootOnZFS#ZFS_Swap_Volume, other bits are from elsewhere. Using both "org.freebsd:swap=on" and /etc/fstab is redundant but doesn't hurt anything.
HTH,
JN
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