Date: Sat, 16 Jan 1999 11:28:50 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: asami@cs.berkeley.edu (Satoshi Asami) Cc: current@FreeBSD.ORG Subject: Re: mounting double-ended SCSI disks Message-ID: <9602.916482530@critter.freebsd.dk> In-Reply-To: Your message of "Sat, 16 Jan 1999 02:20:06 PST." <199901161020.CAA47520@silvia.hip.berkeley.edu>
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>However, if I try to mount it from B read-only while A is mounting it >read-write, it succeeds. This looks dangerous, as A writing data onto >the disk could cause B's cache to go stale without B knowing it. Is >it a good idea to allow read-only mounts of a dirty filesystem anyway? >(The filesystem could be corrupted, right?) UFS/FFS doesn't expect anybody else to muck about on the device while they have it open, and violating that is a bad idea, I cannot tell if it would lead to panics, but I can imagine a couple of ways it would become quantum mechanical in such a setup. A couple of filesystem have been designed over the years which allow for multiple machine access, but they tend to have lousy performance because of caching being so inefficient. One of the better implementations cheated, they stored the stuff in an Oracle database on a third machine, but used a filesystem interface... -- Poul-Henning Kamp FreeBSD coreteam member phk@FreeBSD.ORG "Real hackers run -current on their laptop." FreeBSD -- It will take a long time before progress goes too far! To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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