Date: Sat, 04 Dec 1999 12:44:43 -0800 From: Kirk McKusick <mckusick@flamingo.McKusick.COM> To: Mike Smith <msmith@freebsd.org> Cc: match@elen.utah.edu, current@freebsd.org Subject: Re: Mounting one FS on more than one system Message-ID: <199912042044.MAA05073@flamingo.McKusick.COM> In-Reply-To: Your message of "Sat, 04 Dec 1999 13:53:26 PST." <199912042153.NAA04820@mass.cdrom.com>
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To: match@elen.utah.edu cc: current@freebsd.org, mckusick@mckusick.com Subject: Mounting one FS on more than one system In-reply-to: Your message of "Sat, 04 Dec 1999 10:10:20 MST." <19991204170659.B8DEE5420@ee.elen.utah.edu> Date: Sat, 04 Dec 1999 13:53:26 -0800 From: Mike Smith <msmith@freebsd.org> (moved to -current where there are more eyes that are interested) > P.S. Mike, at comdex I spoke to you some about clustering two > computers and one RAID array, remember? You mentioned that > someone had pursued that avenue some, perhaps not to a working > solution, but I don't remember who. Can you (or anyone else) point > me to the guilty parties? We would like to pick up the work and run > with it for a while. Yup, I remember. I also remember going through my stack of business cards wondering whether I remembered to get one from you; obviously not. 8) The sticking issue that we discussed was allowing more than one system to mount a given filesystem; I seemed to recall that Kirk has spoken about this before, and there may be some folks here (or Kirk himself, also copiedd) who may have some more input on the topic. Once this is resolved, everything else is (relatively!) straightforward... -- \\ Give a man a fish, and you feed him for a day. \\ Mike Smith \\ Tell him he should learn how to fish himself, \\ msmith@freebsd.org \\ and he'll hate you for a lifetime. \\ msmith@cdrom.com Mounting on more than one system is generally problematical unless you are willing to have all systems read-only. The problem is cache coherence between the machines. If one changes a block, the other machines will not see it. Basically, this is why we have the NFS filesystem. That lets a disk be mounted on one machine, but shared out to others. If you wanted to write a protocol that would allow for multiple machines, then you would need to have some central coordinator running some sort of coherency protocol with a complexity akin to that of NFS. Kirk McKusick To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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