filesystem becomming read only

Theodore Tso tytso at
Sun Jan 28 23:10:13 UTC 2007

On Sun, Jan 28, 2007 at 04:38:12PM -0600, Tim Rupp wrote:
> I'm looking for advice/help in tracking down a problem with a new system
> I've purchased.
> I have a beige box server with a Gigabyte GA-M51GM-S2G motherboard. It
> has the nVidia MCP51 SATA controller with 3 250 gig Western Digital hard
> drives attached to it.
> It seems that when doing a considerable amount of file writing, the
> filesystem will become read-only. See attached dmesg output.

According to the dmesg output, the filesystem is getting remounted
read-only because the kernel detected an inconsistency in the block
allocation bitmaps.  Basically, a block that was in use and getting
freed (due to a file getting deleted) was found to be already marked
as not in use in the block bitmap.  This is very dangerous, since a
corrupted block allocation bitmap can result in data loss when a block
gets used by two different files, and the contents of part of the
first file gets overwritten by the second.  Hence, ext3 remounted the
filesystem read-only in order to protect your data from getting (more)

The question then is why is this happening.  If you run e2fsck and it
finds nothing wrong, then that means it was the in-core memory that
was corrupted --- so the data was correct on disk, but when it was
read from disk to memory, it had gotten corrupted somehow (another
good reason for ext3 to mark the filesystem read-only; to prevent the
corrupted data from getting written back to disk).

In any case, given that you've checked the memory, it does rather seem
to narrow it down to either SATA cables, the disk drives, or the SATA
controller, roughly in that order of probability.  The SATA cables are
probably the cheapest to try replacing first.  I suppose there is a
chance that there it's a hardware device driver or kernel issue.  You
might want to ask on LKML or on the Ubuntu support forums if there are
any known issues wit the nVidia SATA controller driver.

Good luck,

						- Ted

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