Date: Tue, 22 Jan 2013 07:33:59 -0700 From: Scott Long <scottl@samsco.org> To: Borja Marcos <borjam@sarenet.es> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: RFC: Suggesting ZFS "best practices" in FreeBSD Message-ID: <565CB55B-9A75-47F4-A88B-18FA8556E6A2@samsco.org> In-Reply-To: <314B600D-E8E6-4300-B60F-33D5FA5A39CF@sarenet.es> References: <314B600D-E8E6-4300-B60F-33D5FA5A39CF@sarenet.es>
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On Jan 22, 2013, at 4:03 AM, Borja Marcos <borjam@sarenet.es> wrote: > (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 >=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 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 > 2- RAID cards. >=20 > Simply: Avoid them like the pest. ZFS is designed to operate on bare = disks. And it does an amazingly good job. Any additional software layer = you add on top will compromise it. I have had bad experiences with "mfi" = and "aac" cards.=20 >=20 Agree 200%. Despite the best effort of sales and marketing people, RAID = cards do not make good HBAs. At best they add latency. At worst, they = add a lot of latency and extra failure modes. Scott
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