Date: Thu, 12 May 2011 10:45:01 +0200 From: =?iso-8859-2?Q?=A9imun_Mikecin?= <numisemis@gmail.com> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: ZFS: How to enable cache and logs. Message-ID: <A3B76BB6-49DC-4C2F-BD2B-9A0C62F4D24C@gmail.com> In-Reply-To: <20110512083429.GA58841@icarus.home.lan> References: <4DCA5620.1030203@dannysplace.net> <4DCB455C.4020805@dannysplace.net> <alpine.GSO.2.01.1105112146500.20825@freddy.simplesystems.org> <20110512033626.GA52047@icarus.home.lan> <4DCB7F22.4060008@digsys.bg> <20110512083429.GA58841@icarus.home.lan>
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On 12. svi. 2011., at 10:34, Jeremy Chadwick wrote: >=20 > I had no idea the primary point of a SLOG was to deal with = applications > that make use of O_SYNC. I thought it was supposed to improve write > performance for both asynchronous and synchronous writes. Obviously = I'm > wrong here. If the application is not using O_SYNC, write operation returns to the = app before the data is actually written. > What guarantee is there that the intent log -- which is written to the > disk -- actually got written to the disk in the middle of a power > failure? There's a lot of focus there on the idea that "the intent = log > will fix everything, but may lose writes", but what guarantee do I = have > that the intent log isn't corrupt or botched during a power failure? I expect that checksumming also works for ZIL (anybody knows?). If that = is the case, corruption would be detected, but you will have lost data = unless you are using mirrored slog devices.
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