Date: Wed, 29 Apr 1998 21:08:32 +0200 (MET DST) From: Wilko Bulte <wilko@yedi.iaf.nl> To: grog@lemis.com (Greg Lehey) Cc: hans@artcom.de, freebsd-hackers@FreeBSD.ORG Subject: Re: FreeBSD HA configuration / Ethernet address takeover Message-ID: <199804291908.VAA14966@yedi.iaf.nl> In-Reply-To: <19980429111546.54200@papillon.lemis.com> from Greg Lehey at "Apr 29, 98 11:15:46 am"
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As Greg Lehey wrote... > On Sat, 25 April 1998 at 15:11:21 +0200, Hans Huebner wrote: > > Hello there, > > > > we're running some of our critial LAN services (NIS, DNS, mail etc.) on > > FreeBSD. The systems are quite stable, but from time to time we need to > > take a system down for maintenance purposes. Also, hardware problems can > > cause unplanned down times. ... > 2. SCSI takeover. > > Tandem has had a number of strategies. None use two host adaptors > on a string. The one used by the (now defunct) S2 range of triple > modular redundant machines is closest to what you suggest: it uses > a dual ported host adaptor, but only one IO processor controls the > host adaptor at any one time. Since the system as a whole doesn't > fail, there's no need to perform an fsck on the disks at takeover. > > I can't see a good solution in using two host adaptors on two > different machines connected to a single string. As long as the > second machine doesn't have access to the first machine's buffer > cache, data can get lost, and a takeover must involve an fsck. > The overhead of fsck could go into several minutes, much longer > than the time that the application layer takes to try another IP HA solutions without some kind of log based FS are in fact quite non-sensical if you have > 1 machine. > address. I don't think that this would make much sense from an > availability standpoint, though it obviously makes sense to > recover the file systems and make them available on another > machine if the first machine is going to be out of commission for > any length of time. > > What makes more sense is to replicate the data across multiple > systems. Possibly a software layer like the vinum volume manager > would be able to perform this function: put one copy of the data > on the local machine, another on one or two other machines via NFS > or some other protocol, and always read from the local machine. > As long as the write rate is not too high, this should allow for > higher availability. You could go for a RAID box, with dual raidcontrollers, each with a dual host port. If one of the SCSI 'rails' fails you can access the data via the surviving port. This solves the single point of failure of the SCSI buses, the host adapters and the raidcontrollers themselves. It does not, however, solve an important point: $$$ ;-) Wilko _ ______________________________________________________________________ | / o / / _ Bulte email: wilko @ yedi.iaf.nl |/|/ / / /( (_) Arnhem, The Netherlands WWW: http://www.tcja.nl ______________________________________________ Powered by FreeBSD __________ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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