Date: Wed, 27 Feb 2019 19:24:24 +0000 From: Matt Churchyard <matt.churchyard@userve.net> To: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: ZFS memory use (arc limit) Message-ID: <d0159ae35615451386af3781e3aa501a@SERVER.ad.usd-group.com>
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Hello, What's the current best practices for handling memory use for ZFS ARC? I've been a ZFS user for over 10 years starting with v15 pretty much back w= hen it first appeared. Very quickly I adopted the attitude of immediately limiting ARC manually vi= a sysctl, as I seemed to get guaranteed swap issues otherwise. Over the yea= rs I've seen references to other people seeing the same issues, various wor= k on ZFS memory use, but I've never relied on the system to sort itself out= and always just hard limited it by default. Just this week I installed a new system (11.2-REL) with 12GB RAM (not a hug= e amount but more than most my FreeBSD systems) that does nothing else othe= r than NFS sharing. I never got round to limiting the ARC and thought it wo= uld probably be alright considering how mature the ZFS support is these day= s. I did check the sysctl and it seemed to be set around 11GB or so. Just o= ver 24 hours after booting the NFS shares went down and a check of dmesg sh= ows the familiar "x was killed; out of swap space" errors. Swap space is 4G= B, which could probably be higher, but I've never seen it above a few MB in= use. (Maybe I need to set it the same as RAM?) As such, it seems that it's still absolutely vital that the admin sets a ha= rd limit on ARC, leaving enough headroom for whatever applications are bein= g run on the system? Is this recommended, or is there something I'm not doing right...? Regards, Matt Churchyard
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