From owner-freebsd-fs@freebsd.org Fri Nov 6 06:24:24 2015 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 061FEA27509 for ; Fri, 6 Nov 2015 06:24:24 +0000 (UTC) (envelope-from josh@tcbug.org) Received: from mailman.ysv.freebsd.org (mailman.ysv.freebsd.org [IPv6:2001:1900:2254:206a::50:5]) by mx1.freebsd.org (Postfix) with ESMTP id DC18312E9 for ; Fri, 6 Nov 2015 06:24:23 +0000 (UTC) (envelope-from josh@tcbug.org) Received: by mailman.ysv.freebsd.org (Postfix) id D97FBA27508; Fri, 6 Nov 2015 06:24:23 +0000 (UTC) Delivered-To: fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id BF36EA27507 for ; Fri, 6 Nov 2015 06:24:23 +0000 (UTC) (envelope-from josh@tcbug.org) Received: from out4-smtp.messagingengine.com (out4-smtp.messagingengine.com [66.111.4.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 92E5A12E8 for ; Fri, 6 Nov 2015 06:24:22 +0000 (UTC) (envelope-from josh@tcbug.org) Received: from compute1.internal (compute1.nyi.internal [10.202.2.41]) by mailout.nyi.internal (Postfix) with ESMTP id 2991820242 for ; Fri, 6 Nov 2015 01:24:21 -0500 (EST) Received: from frontend1 ([10.202.2.160]) by compute1.internal (MEProxy); Fri, 06 Nov 2015 01:24:21 -0500 DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:content-type :date:from:in-reply-to:message-id:mime-version:references :subject:to:x-sasl-enc:x-sasl-enc; s=smtpout; bh=EoLDP7rTRF12id9 e83v9zZeQH1Q=; b=VP8q2YPgdDPPngR04WG3zReLKjSSrhCbo61QaiNG0LBu56l A9/MIqvLEuVtdKRllImOXLkAX/XNHY/EB8geddhpQZragujfxurc0JmEn21kbK2i /Bdds7XMNw1yi24I54EiAA9r3/fpDrmq0IJEKX6x/SCUUQej0PoLyGdil+Pg= X-Sasl-enc: 0Nh0t4QQ8uUJKliPgMxee/Te8USCB3FZjuzA3kXUlH8D 1446791060 Received: from [192.168.8.142] (184-158-23-49.dyn.centurytel.net [184.158.23.49]) by mail.messagingengine.com (Postfix) with ESMTPA id C808BC016DB; Fri, 6 Nov 2015 01:24:20 -0500 (EST) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (1.0) Subject: Re: hast exec vs devd for handling CARP events From: Josh Paetzel X-Mailer: iPhone Mail (13B143) In-Reply-To: <20151103173526.GA17299@mail.michaelwlucas.com> Date: Fri, 6 Nov 2015 00:24:20 -0600 Cc: fs@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: <64BC4405-50B7-424F-9CB6-00A6475C4204@tcbug.org> References: <20151103173526.GA17299@mail.michaelwlucas.com> To: "Michael W. Lucas" X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 06 Nov 2015 06:24:24 -0000 Both hast and carp have an amazing propensity to go split brain. This has de= vastating affects. Hundreds of years ago sailing vessels could determine their latitude by shoo= ting the sun with an astrolabe and knowing the precise time. (You can also c= alculate the time if you know your latitude and have an astrolabe) The wisdom of that time was go to sea with one clock or three. If you have o= ne clock you have no choice but to believe it. If you have three you believe= the two that agree. If you have two clocks and they disagree you are in a w= orld of hurt. Such is it with computers too. You really need three systems to do HA. The b= est you can do with two systems is require a positive ACK from both nodes be= fore one node will take over, otherwise you are forced to go passive-passive= and require administrative action to proceed. Any other strategy will event= ually hit a situation where it goes split brain. If you are in a directly connected universe you can use SPC-3 SCSI reservati= ons to lock the disks and prevent the nodes from destroying the storage. In a= hast universe you really need quorum. Thanks, Josh Paetzel > On Nov 3, 2015, at 11:35 AM, Michael W. Lucas w= rote: >=20 > Hi, >=20 > There's lots of recipes out there for HAST failover based on devd. >=20 > HAST also has the ability to run scripts on events, with the exec > function in hast.conf. >=20 > It *seems* it make more sense to have HAST mount filesystems and start > processes when it claims the master role for a resource, as opposed to > triggering that mount via a devd event and waiting for HAST to perform > the switch. >=20 > Thanks for any insight. I'm researching the "specialty filesystems" > book, and want to give the best advice. >=20 > =3D=3Dml >=20 > --=20 > Michael W. Lucas - mwlucas@michaelwlucas.com, Twitter @mwlauthor=20 > http://www.MichaelWLucas.com/, http://blather.MichaelWLucas.com/ > _______________________________________________ > freebsd-fs@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org"