Date: Mon, 24 Jul 2000 13:48:52 -0700 From: Jack Rusher <jar@integratus.com> To: mjacob@feral.com Cc: freebsd-arch@FreeBSD.ORG Subject: Re: SANs, disks, & devfs Message-ID: <397CABB4.1CAAC7C3@integratus.com> References: <Pine.BSF.4.10.10007240442030.55035-100000@beppo.feral.com>
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Matthew Jacob wrote: > > I think that vinum is already good, like VxVM also, in that once you label a > disk (i.e., borg it into vinum), it's boot-time to boot-time address becomes > can become less relevant. Yes, there is self descriptive meta data on VxVM and vinum drives. However, you need some way to tell vinum which drives to eat. I think it would be useful to be able to specify this in a WWN aware fashion. > The whole /dev/dsk/XXX goop was/is a complete disaster in that it half-assed > mushes together some bogus fixed name and address semantics into a symlink > to try and give you some location info in the 'friendly' name (as opposed > to the completely unambiguous physical pathname of the 'all-singing, There are some problems with trying to do this with WWN (or any other serial number) as the only entry point to the device. Namely, you can't be sure that the device will have any such serial number. Also, it makes it a pain in the ass for the casual user if they can't just say "/dev/da0, please." > I think that the constancy of the /dev/daX namespace is relevant only as > long as that is the name in /etc/fstab. There are other issues having to do with what happens when you pull a disk out and copy the contents onto another drive (upgrade to bigger primary disk, for instance). You want to just stick the drive back in the machine and have everything boot and work normally. This only works if the fstab looks at the first SCSI drive by a positional name. The other option is to use disklabels (instead of disk serial numbers) to identify the disks. You can provide a label copy tool to clone a disk, but you run into trouble when you have two disks that are clones of one another in the same system. You also have trouble if one of the disks is the Windows/Linux/whatever partition of your workstation and has a label scheme that doesn't play nice with the BSD scheme. What do you call that disk in the device tree? All I am trying to illustrate here is that there are some cases where it is better to have absolute names and some cases where positional abstraction is the right answer. It would be nice if we could have a compromise of the two techniques that lets you look at your storage in the way that makes the most sense for your application. -- Jack Rusher, Senior Engineer | mailto:jar@integratus.com Integratus, Inc. | http://www.integratus.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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