fsck reports errors on clean filesystem (mounted rw)

Bruce Cran bruce at cran.org.uk
Sun Sep 12 21:34:20 UTC 2010

On Sun, 12 Sep 2010 16:16:53 -0500 (CDT)
Robert Bonomi <bonomi at mail.r-bonomi.com> wrote:

> There are exactly _four_ possible causes of file-system
> inconsistencies. 1) You can have an unexpected loss of power, where
> the CPU stops working before it as time to write the above-mentioned
> 'memory-resident' data to disk.  There are  sub-classes of tis event,
> to distinguish between A utility company outage, somebody
> accidentally 'pulling the plug', be it litterally, or the power
> on/off switch, and somebody itting the 'reset' button.  They all ave
> te same effect,  the processor can't get te 'current' data in memory
> out to the disk. 2) you can hve a catastropic O/S failure -- a system
> 'crash' -- were the O/S has discovered an internal inconsistency.
> _IT_ doesn't trust its own data enough to keep running, and takes
> 'the lesser of two evils' route of *not* writing "known to be
> suspect" data over the out-of-date data on the disk.
>   3) 'bit rot' on the phyiscal media itself.  Where what gets read
> back is *not* what was written there earlier.  Modern disk drives
> detect this inside the controller and use embedded ECC info to give
> the 'right' data back, while alerting that the problem exists.
>   4) "Hardware failures" of any of a variety of sorts -- flakey power
> supply, bad RAM memory, failing controller cipes, etc.

5. An bug in the filesystem code. I've been seeing UFS corruption in
recently -current, as have others, which isn't associated with crashes
or bad media.

Bruce Cran

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