Date: Tue, 22 Jan 2013 22:45:26 -0700 From: Scott Long <scottl@samsco.org> To: David Xu <davidxu@freebsd.org> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: RFC: Suggesting ZFS "best practices" in FreeBSD Message-ID: <5DD4A455-A351-4676-979B-4D7199F0FA1C@samsco.org> In-Reply-To: <50FF7764.2020803@freebsd.org> References: <314B600D-E8E6-4300-B60F-33D5FA5A39CF@sarenet.es> <565CB55B-9A75-47F4-A88B-18FA8556E6A2@samsco.org> <50FF7764.2020803@freebsd.org>
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On Jan 22, 2013, at 10:38 PM, David Xu <davidxu@freebsd.org> wrote: > On 2013/01/22 22:33, Scott Long wrote: >>=20 >> On Jan 22, 2013, at 4:03 AM, Borja Marcos <borjam@sarenet.es> wrote: >>=20 >>> (Scott, I hope you don't mind to be CC'd, I'm not sure you read the = -FS mailing list, and this is a SCSI//FS issue) >>>=20 >>>=20 >>>=20 >>> Hi :) >>>=20 >>> Hope nobody will hate me too much, but ZFS usage under FreeBSD is = still chaotic. We badly need a well proven "doctrine" in order to avoid = problems. Especially, we need to avoid the braindead Linux HOWTO-esque = crap of endless commands for which no rationale is offered at all, and = which mix personal preferences and even misconceptions as "advice" (I = saw one of those howtos which suggested disabling checksums "because = they are useless"). >>>=20 >>> ZFS is a very different beast from other filesystems, and the setup = can involve some non-obvious decisions. Worse, Windows oriented server = vendors insist on bundling servers with crappy raid controllers which = tend to make things worse. >>>=20 >>> Since I've been using ZFS on FreeBSD (from the first versions) I = have noticed several serious problems. I try to explain some of them, = and my suggestions for a solution. We should collect more use cases and = issues and try to reach a consensus. >>>=20 >>>=20 >>>=20 >>> 1- Dynamic disk naming -> We should use static naming (GPT labels, = for instance) >>>=20 >>> ZFS was born in a system with static device naming (Solaris). When = you plug a disk it gets a fixed name. As far as I know, at least from my = experience with Sun boxes, c1t3d12 is always c1t3d12. FreeBSD's dynamic = naming can be very problematic. >>>=20 >>=20 >> Look up SCSI device wiring in /sys/conf/NOTES. That's one solution = to static naming, just with a slightly different angle than Solaris. I = do agree with your general thesis here, and either wiring should be made = a much more visible and documented feature, or a new mechanism should be = developed to provide naming stability. Please let me know what you = think of the wiring mechanic. >>>=20 >>>=20 >=20 > I am curious, because we already have devfs, why do not the driver = create device entry like following ? >=20 > /dev/scsi/bus0/target0/lun0/ada0 > /dev/scsi/bus0/target0/lun0/ada0s1 > /dev/scsi/bus0/target0/lun0/ada0s2 > ... >=20 > This will eliminate the needs of hints. >=20 The problem is that this structure is east for computers to manipulate, = but hard for humans to manipulate. One thing that could be done with = devfs, however, is to create device aliases. i.e.: crw-r----- 1 root operator 0x86 Jan 2 23:00 c0b0t1l0 lrwxr-xr-x 1 root wheel 6 Jan 2 23:00 da0 -> c0b0t1l0 This gets hairy because aliases then need to be made for partitions, = unless some sort of transparent translator is created in devfs. It also = gets complicated because you still need to arbitrate the controller = numbering (the 'c0' in the above example), so wiring might still be = needed. Scott
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