Date: Sat, 25 Apr 1998 20:12:51 -0700 From: Mike Smith <mike@smith.net.au> To: hans@artcom.de (Hans Huebner) Cc: mike@smith.net.au, freebsd-hackers@FreeBSD.ORG Subject: Re: FreeBSD HA configuration / Ethernet address takeover Message-ID: <199804260312.UAA01761@antipodes.cdrom.com> In-Reply-To: Your message of "Sat, 25 Apr 1998 22:40:45 %2B0200." <m0yTBkb-00000nC@mail.artcom.de>
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> Hello Mike, > > In article <199804251913.MAA00572@antipodes.cdrom.com> you write: > >None of the filesystems supported by FreeBSD are suited to multiple > >consumers, so I'm not sure what you would hope to gain from such a > >thing. If your intention was to be able to swap the disk set to the > >replacement server, you'd be better off with a SCSI switch. > > A common bus would minimize the downtime of a HA pair. Also, such a > mechanism could allow for easy sharing of removeable media drives. I don't see how having a common bus would minimize downtime in any meaningful fashion, without a failsafe means of fallover. This isn't going to be available until you start looking at high-end RAID controllers with multiple host ports. In the bad old days when storage was expensive, this was popular. These days, time costs more than hardware. > > FreeBSD > >systems don't tend to take very long to come up when suitably configured, > > .... and orderly shut down. If the system owning the disks went down in a mess, the disks have to be cleaned regardless. If you want to avoid this, sharing disks is counterproductive. > >so you could well just shut the primary server down, flip the SCSI > >switch and then hit enter at the boot: prompt on your warm spare. > > This is fine as long as an operator is present. Also, the downtime > will be considerably longer than the time a ethernet address failover > would require, since the latter involves no manual switching of > SCSI busses and booting of servers. Are you arguing for or against shared SCSI busses? Ethernet address fallover requires the spare be hot, which precludes sharing a bus with the active server. > >As others have suggested, though, all of the services that you've > >described already support redundant servers. > > I'm aware of that. I'd prefer failing over the ethernet address > because it would also simplify the implementation of redundant > servers. This is because the server processes themselves only need > to support orderly shutdown. Designing a high availabilty mechanism > at the application level is bound to be more problematic than failing > over the server processes at the operating system level. Not necessarily. But your later points regarding the quality of current client implementations support hacks at the server level in order to achieve an effective workaround, yes. > Failing over the ethernet address is completely transparent to the > clients (at least with stateless server protocols), which is a big > plus given the stupidity of commonly used clients. Agree. -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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