Date: Mon, 24 Apr 2000 09:59:20 -0700 From: David Greenman <dg@root.com> To: sthaug@nethelp.no Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: Safe mounting of one file system on multiple hosts? Message-ID: <200004241659.JAA08902@implode.root.com> In-Reply-To: Your message of "Mon, 24 Apr 2000 17:15:00 %2B0200." <70070.956589300@verdi.nethelp.no>
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>I have a RAID system from Nexsan (www.nexsan.com), which is basically >two CMD CDR-5644 controllers in a hot-standby configuration. The system >has two host channels, and two disk channels. I have two different hosts >connected to the two hosts channels. > >Normally, I would configure two (or more) RAID sets, and have each RAID >set dedicated to one host (visible on only one of the host channels). >Each RAID set appears to the host as one disk - and can be partitioned, >newfs'ed etc. with normal FreeBSD tools. This works fine. > >However, I also have the *option* of making all RAID sets visible on >*both* host channels. I don't want to try read/write mounting one RAID >set on two hosts - but can I safely read/write mount the RAID set (its >corresponding file system(s)) on one host, and mount it readonly on the >other host? I guess the basic question is: Will a readonly mount of a >file system lead to *zero* writes to this file system? It might work if you use softupdates, but it won't work if you don't since the state of the on-disk filesystem metadata isn't always going to be consistent due to defered writes. The read-only machine will also have stuff in it's own cache which won't be kept updated and will certainly interfere with the correct view of things (which probably means that it won't work with softupdates, either). Of course, if both servers mount it read-only, then you'll be fine. -DG David Greenman Co-founder/Principal Architect, The FreeBSD Project - http://www.freebsd.org Creator of high-performance Internet servers - http://www.terasolutions.com Pave the road of life with opportunities. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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