Date: Fri, 18 May 2012 09:55:24 -0700 From: Trent Nelson <trent@snakebite.org> To: "araujo@FreeBSD.org" <araujo@FreeBSD.org> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: Mirror of Raidz for data reliability Message-ID: <CBDBEF7C.2B265%trent@snakebite.org> In-Reply-To: <CAOfEmZj9mPnU%2BxgYP8qNWdPL_seqO7vxvwB-ZNOr3dGEUW5dbQ@mail.gmail.com>
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Hi Marcelo,=20 On 5/17/12 9:34 PM, "Marcelo Araujo" <araujobsdport@gmail.com> wrote: >2012/5/17 George Kontostanos <gkontos.mail@gmail.com> > >> On Thu, May 17, 2012 at 1:52 PM, George Kontostanos >> <gkontos.mail@gmail.com> wrote: >> >> >> Ok, after reading more carefully your first post I realized what you >> are trying to do. >> >> 2 Machines, 2 different controllers. Yet interconnected. So, in a way >> both machines would be able to see both controllers. >> >> 2) Both machines have to be online and the pool has to be mounted >> readonly on the standby! You don't want both of them to accidentally >> write at the same pool. >> >> >Not no.You can use Devd to start some scripts to mount the FS in another >machine or something like that. >But I can't be focused only in this scenario, I believe there are much >more >application for it. I'm in a similar situation with Snakebite. I have two boxes that can see a common set of disks (via FC SAN). I'm interested in failover, but like you, I don't want to use HAST -- why duplicate data when both machines can access the disks? I came across these articles yesterday, which are pretty neat: CARP and devd on FreeBSD: http://blather.michaelwlucas.com/archives/224 Automated CARP/HAST Failover: http://blather.michaelwlucas.com/archives/241 (Both of those posts reference lots of other articles; all of which I also found to be very good reads.) The author uses CARP/devd/HAST to automate failover and rebuild. Our situation is a little different because we don't want/need to use HAST. So, my thinking is=8A because both machines can see all disks, the master could import the zpool as normal, and the slave could import it read-only. (Or not import it at all...) Then, when CARP detects that the master has failed, some script will kick in on the slave (via devd?) and re-mount the zpools read-write. (Or import them for the first time.) That approach seems like a feasible starting point to me. It'll take a bit of fiddling of course, as FreeBSD isn't really set up to utilize ZFS like that. I'm planning on having my own /etc/rc.* type scripts that manually import/load zpools, rather than using /etc/rc.conf's zfs_enable=3D"YES" (which will definitely break things). Now the only thing that confuses me about your original e-mail is with regards to adding raidz vdevs. Can I enquire what you'll actually be doing with the zpools once they're loaded? I.e. You mentioned failover; what services will you be providing (NFS? Apache?) that you want to fail over? In my case, I'd *like* to be able to offer NFS, iSCSI and FC-target-mode in such a way that if the master dies, failover to the slave is automatic and transparent. At least, that's the ideal scenario :-) It'll sure take a bit of fiddling/hacking to get that working. Regards, Trent.
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