Date: Mon, 21 Jul 2014 11:16:13 -0400 From: Paul Kraus <paul@kraus-haus.org> To: freebsd-questions@freebsd.org Subject: SWAP / ZFS / SSD question Message-ID: <D38CF9C2-13AD-4E5C-9265-3010A51AB65A@kraus-haus.org>
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Hi all, I=92ve got a box running Freebsd 9.1 with VirtualBox and have = run into a couple odd hangs. The system is a SuperMicro with two = quad-core Xeon, 32GB RAM, and 3 1TB SAS drives mirrored via an internal = LSI 2208 controller (the drives are in JBOD mode) via ZFS. The system = is all ZFS with a 32GB zvol for swap. I am occasionally running into the dreaded "kernel: swap_pager: = indefinite wait buffer: bufobj: 0=94 issue. In the past it was always = when I was either adding a VM or changing a VM=92s configuration. I = assumed low RAM. But it hit last night (at 03:00 this morning in fact) = and nothing was changing at that time. There was about 770MB RAM free = and the ZFS ARC was using about 4GB, so the system was not really under = heavy memory pressure at the time. In order to reduce the impact, until we put a more permanent fix = in place, I have set sync=3Ddisable for the zvol =85 I figure that if = the system crashes and I lose a swap write I really don=92t care (I am = assuming here that swapd commits it=92s writes as sync). Our long term plan is a change in overall architecture that will = separate storage and compute services and have multiple compute nodes. = We started with one box assuming we would grown to more than one as the = business need arose. So our mid-term plan is to install a dedicated swap = device. The question is whether swapd (under 9.1) will be happy with an = SSD or whether there are unintended consequences to that route. Small = SSDs are cheap enough these days, we really don=92t need more than 32GB = (64GB if we are feeling extravagant). I know about the major performance differences between SSD = vendors and models (I heard all about that on the various ZFS lists I = subscribe to), so we will have to choose an SSD carefully. -- Paul Kraus paul@kraus-haus.org
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