Date: Fri, 29 Jan 2016 12:06:16 -0600 From: Graham Allan <allan@physics.umn.edu> To: freebsd-fs@freebsd.org Subject: quantifying zpool performance with number of vdevs Message-ID: <56ABAA18.90102@physics.umn.edu>
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In many of the storage systems I built to date I was slightly conservative (?) in wanting to keep any one pool confined to a single JBOD chassis. In doing this I've generally been using the Supermicro 45-drive chassis with pools made of 4x (8+2) raidz2, other slots being kept for spares, ZIL and L2ARC. Now I have several servers with 3-4 such chassis, and reliability has also been such that I'd feel more comfortable about spanning chassis, if there was worthwhile performance benefit. Obviously theory says that iops should scale with number of vdevs but it would be nice to try and quantify. Getting relevant data out of iperf seems problematic on machines with 128GB+ RAM - it's hard to blow out the ARC. It does seem like I get possibly more valid-looking results if I set "zfs set primarycache=metadata" on my test dataset - it seems like this should mostly disable the ARC (seems to be borne out by arcstat output, though there could still be L2ARC effects). Wonder if anyone has any thoughts on this, and also on benefits/risks of moving from 40-drive to 80- or 120-drive pools. Graham --
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