Date: Sun, 12 Sep 2010 22:34:06 +0100 From: Bruce Cran <bruce@cran.org.uk> To: Robert Bonomi <bonomi@mail.r-bonomi.com> Cc: cronfy@gmail.com, freebsd-questions@freebsd.org Subject: Re: fsck reports errors on clean filesystem (mounted rw) Message-ID: <20100912223406.00005904@unknown> In-Reply-To: <201009122116.o8CLGr0l016533@mail.r-bonomi.com> References: <201009122116.o8CLGr0l016533@mail.r-bonomi.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sun, 12 Sep 2010 16:16:53 -0500 (CDT) Robert Bonomi <bonomi@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 suspect" data over the out-of-date data on the disk.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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20100912223406.00005904>