Date: Fri, 05 Sep 2008 13:23:37 +0100 From: Pete French <petefrench@ticketswitch.com> To: pjd@FreeBSD.org Cc: freebsd-geom@freebsd.org Subject: Re: Could someone take a look at a small patch to gmirror ? Message-ID: <E1KbaLh-000MLo-3R@dilbert.ticketswitch.com> In-Reply-To: <20080905073517.GA4021@garage.freebsd.pl>
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> The possibility of setting priority only on insert time is a bit > limiting (and mentioned in BUGS section in gmirror(8)), but I think the > better way to do it is to just extend configure subcommand to allow > priority change, eg. > > # gmirror label foo da0 da1 > # gmirror configure -p 7 foo da1 > > We could also add -p option to label subcommand to define starting > priority, but I'm not sure about that one. > > Would you like to work on such a patch maybe? Actually, yes - indeed I was thinking of doing so. But the 'prefer-low' is still required for when you change the mirror over in the situation I decsribed, so the patch is still needed. As an example, I have two discs in a mirror, priorityies 1 and 0 on machines server1 and server0. Normally I use server1 and mount the drive from server0 using ggate. Prefer keeps all my reads to disc with priority 1 so it all performs nicely. But if I want to do some maintenenace on server 1 then I switch to using server 0, and swap over the mounts - i.e. use ggate on server 0 to mount the drive from server 1 in the mirror. Note that I am not changing any of the drives, simply where I am running the mirror. So now I want to keep all my reads to drive 0, and hence I need something which will prefer the lower number. The situation described above is my actual live setup - I am running mysql on top of the mirrored pair, and I switch the machine being used when I wish to upgrade the mysql software. This is why I added the prefer-low algorithm. I will, of course, look at the patch to configure too, but I would hope that you can see why having the inverse algorithm is useful and will consider acceopting that change too, thanks, -peete.
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