Re: Block-level CRC checks

From: Chuck McDevitt <cmcdevitt(at)greenplum(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, decibel <decibel(at)decibel(dot)org>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, "jd(at)commandprompt(dot)com" <jd(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2009-12-04 22:47:15
Message-ID: 2106D8DC89010842BABA5CD03FEA4061013686B5E9@EXVMBX018-10.exch018.msoutlookonline.net
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A curiosity question regarding torn pages: How does this work on file systems that don't write in-place, but instead always do copy-on-write?

My example would be Sun's ZFS file system (In Solaris & BSD). Because of its "snapshot & rollback" functionality, it never writes a page in-place, but instead always copies it to another place on disk. How does this affect the corruption caused by a torn write?

Can we end up with horrible corruption on this type of filesystem where we wouldn't on normal file systems, where we are writing to a previously zeroed area on disk?

Sorry if this is a stupid question... Hopefully somebody can reassure me that this isn't an issue.

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