Date: Sat, 18 Sep 2004 23:48:17 +0200 From: Ivan Voras <ivoras@fer.hr> To: Pawel Jakub Dawidek <pjd@FreeBSD.org> Cc: current@FreeBSD.org Subject: Re: gmirror: DIRTY flag? Message-ID: <414CAD21.9060409@fer.hr> In-Reply-To: <20040918185841.GA30151@darkness.comp.waw.pl> References: <414C2E85.6090904@fer.hr> <20040918185841.GA30151@darkness.comp.waw.pl>
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Pawel Jakub Dawidek wrote: > You use ggate as one of your mirror components? Nice:) Indeed very nice. Not a single problem so far. :) > If you export this device over slow link, you can considern changing > balance algorithm to 'prefer', so only local component will be used for > reading. Yes, I tried several algorithms. This is on a test bench machines, and both the disks and network are very slow (udma33, 100mbit E.). The 'load' algorithm actually seems to work best in this setup. In a month or so we're planning to implement this on some beefy hardware, and I'll test it more then. (If anybody's interested, I'll post some "benchmark" results ;) ). > Remember, that 'prefer' algorithm is based on priority, so in your case > ggate0 will be used for reading as component with bigger priority. I was wondering about that: is bigger priority assigned to smaller or bigger number? The way I've expected it, since command line goes like this: # gmirror label myname device1 [device2...] I've expected that device1 would have bigger priority (semantically speaking). > Priority is also important for synchronization. If you have power > failure, component with the biggest priority will be used as a master > component, and all the rest components synchronize to him. What if the master fails? :) I'm expecting this: When device1 fails, I deactivate it from the mirror, (at this time device2 becomes master) and insert another (will it automagically gain priority 3 or I'll need to specify it?). The mirror resynchronises (transferring everything from device2 to the newly inserted one, thus killing the bandwidth for applications?), and device2 keeps the master status. > Command for changing priority for running mirror is missing, but you > can increase priority for local component by doing: > > # gmirror remove netmirror ad2s1e > # gmirror insert -p 2 netmirror ad2s1e > Ok. Since this is a test setup, it really isn't a problem to tear down and rebuild the mirror. Which leads to another question: Is it ok to rebuild mirrors and change device orders/priorities? E.g. if I do: # gmirror label myname device1 device2 # gmirror stop myname # gmirror label myname device2 device1 ... nothing extraordinary is supposed to happen? -- What part of "Ph'nglui mglw'nath Cthulhu R'lyeh wgah'nagl fhtagn" don't you understand?
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