Subject: Re: Large filesystems, yet again
To: None <tech-kern@netbsd.org>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: tech-kern
Date: 02/01/2006 12:18:17
> The filesystem was 8k/64k, too, and at least one person wrote me
> off-list saying "ISTR hearing of issues with [bsize=64k], but I have
> not looked into it at all".

I remade the filesystem with fsize=1k bsize=8k, figuring that was a
very well-tested size combination.

Then I created 418 files of 4G each, split up into five directories:
00/0001 - 00/0099, 01/0100-01/0199, ..., 04/0400-04/0418.  (There's
nothing special about 418; I just had it keep creating files until df
reported at least 90% full, and that's where it happened to stop.)
Each one has distinctive content; given a disk block belonging to any
of them, the content lets me tell which one it belongs to and where it
belongs within that one.

Then I unmounted the filesystem and ran fsck.  No joy.  The fsck output
is quite long and not very regular, so I don't want to quote it all
here.  But it's got lots of "INCORRECT BLOCK COUNT"s and a number of
inodes with "EXCESSIVE BAD BLKS" (or s/BAD/DUP/), a bunch of "PARTIALLY
TRUNCATED INDOE"s (most of which also exhibit "EXCESSIVE DUP BLKS").

Looking (with my own tools and/or dd) at what's actually on the disk,
it appears that the errors are due to trashed indirect blocks.  I
haven't checked them all - that would take a lot of very tedious manual
work - but the ones I spot-checked all are.  The "INCORRECT BLOCK
COUNT"s seem to be indirect blocks that have got filled with zeros; the
BADs and DUPs seem to be indirect blocks filled with nonzero trash.

I'm not sure where to go from here.  Would 3.0 be expected to do
better?  (The machine is still running 2.0.)  If so, can I just drop in
a 3.0 kernel and leave the rest of the machine running 2.0?  That would
make it a lot more practical to test 3.0 quickly.  In particular, can I
use the GENERIC kernel from the 3.0 install ISO, or does that one not
have 2.0 compat in it?

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