Date: Tue, 29 Apr 2003 00:31:28 +0200 (CEST) From: Oliver Fromme <olli@secnetix.de> To: freebsd-stable@FreeBSD.ORG Subject: Re: sharing scsi disk beetween two freesbd's ... Message-ID: <200304282231.h3SMVSX9045949@lurza.secnetix.de> In-Reply-To: <3EADA59D.6050201@esm2.imt-mrs.fr>
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Geoffroy DESVERNAY <dgeo@esm2.imt-mrs.fr> wrote: > Of course, but the two machines are going to be redundant servers, ant > the disc > (an IDE raid array presented as scsi disk) will have to be accessible by > the second server, > in case of failure of the first one... For that kind of setup, I would recommend to use something like a NetApp Filer. It appears as an NFS server by itself, so you can mount it on both of your redundant machines. Even both read+write, if you want. You can even cluster two Filers that mirror each other, so you get an additional level of redundancy. > Isn't there any mechanism that could force the system to flush read > cache on each operation ? No. You could of course build your own fail-over mechanism: During normal operation, host1 mounts the SCSI disk and host2 mounts it via NFS from host1. If host2 detects a failure of host1, it forcibly removes the NFS mount and then mounts the SCSI disk itself. You have to be very careful, though, since there are a few possible pitfalls. > I think the design of scsi bus, which allow 2 'SCSI adapters' (=> 2 > computers) should imply that one disc (or device) can be accessed by two > hosts at the same time... for reading of course :) It might imply that in the _hardware_ level. But you still need support at the OS level (e.g. VM cache subsystem), which FreeBSD does not provide for its UFS/FFS. Regards Oliver PS: I'm not afiliated with NetApp, but I've been using their products and I'm very satisfied with them. -- Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München Any opinions expressed in this message may be personal to the author and may not necessarily reflect the opinions of secnetix in any way. "Now that the Internet has the full spectrum of humanity as users, the technology is showing its weakness: it was designed to be used by friendly, smart people. Spammers, as an example of a class, are neither friendly nor smart." -- Paul Vixie in an interview with Sendmail.net
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