Date: Fri, 23 Sep 2022 15:42:19 -0700 From: David Christensen <dpchrist@holgerdanske.com> To: questions@freebsd.org Subject: Re: data, metadata, backup, and archive integrity and correction Message-ID: <7be8f47b-bfea-ef5a-7b59-2f94f8d310e2@holgerdanske.com> In-Reply-To: <c15361a3f8328583bdab528c5a49bf475a1dfdfa.camel@riseup.net> References: <b027f6af-bf83-2663-b0ef-2480e385b189@holgerdanske.com> <c15361a3f8328583bdab528c5a49bf475a1dfdfa.camel@riseup.net>
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On 9/23/22 07:28, Ralf Mardorf wrote: > On Wed, 2022-09-21 at 03:58 -0700, David Christensen wrote: >> Integrity checking of data and metadata is important -- both for live >> data and, especially, for backups and archives. > > Hi David, > > good to read that I'm not alone :). > > I don't care that much for live data. To loose a few minutes or even a > few days isn't fun, but bearable. Backups and archives can contain a > full life. > > Unfortunately integrity checks are way to often a PITA :(. > > My current strategy is an obsessional neurosis. It's a little bit more a > psychopathological workaround, than a computer technical attempt. > > I have got tons of backups (unfortunately not stored in different > locations, just on different drives) and from time to time I restore > backups or archives using a sandbox, just for testing purpose. Redundancy of backups is a good thing. So is taking backup media out of rotation and archiving it. "Defense in depth." "Don't put all of your eggs in one basket." One of the reasons I wanted storage with built-in integrity checking and correction is because of an experience I had using storage without those features. I believe I was migrating my bulk data from an older, smaller store to a newer, bigger store. I wrote a script to validate the move (using cmp(1)?). I checked the new store against the old store -- okay. I checked the new store against a backup of the old store -- one photograph file differed by a few bits. All versions of the photograph file opened correctly with a viewer. All photographs looked the same on the screen. But, at least one file is corrupt. Which file(s)? I never figured it out. I kept all versions of the file. (And, I have kept all camera media.) David
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