Date: Mon, 15 Dec 1997 19:36:13 +1030 From: Mike Smith <mike@smith.net.au> To: Mike Smith <mike@smith.net.au> Cc: Terry Lambert <tlambert@primenet.com>, bgingery@gtcs.com, hackers@FreeBSD.ORG Subject: Re: blocksize on devfs entries (and related) Message-ID: <199712150906.TAA00961@word.smith.net.au> In-Reply-To: Your message of "Mon, 15 Dec 1997 18:12:06 %2B1030." <199712150742.SAA01554@word.smith.net.au>
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> > > > Consider a system running soft updates, in the face of a power failure, > > with a two block write crossing a cylinder boundry. This will result > > in a seek. All but the most modern drives (which can power track buffer > > writes and a seek through rotational energy of the disk) will fail to > > commit the write properly. > > Unfortunately, the above reasoning is soggy. In the face of a power > failure, there is no guarantee that a given block will be completely > updated, so the current "guaranteed atomicity" for single-block writes > doesn't exist. Oops. I'm the one who's wet here; I see the assumption now - block is not written, block is corrupt, block is written are all detectable states. This presumes there's no way for the device to present a block that's been only partially updated, which is reasonable. mike
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