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kern/45982: LFS metadata space estimate can cause false "filesystem full" condition
>Synopsis: LFS metadata space estimate can cause false "filesystem full"
>Arrival-Date: Sat Feb 11 06:15:01 +0000 2012
>Originator: Konrad Schroder
>Release: 5.99.64 userland (including RUMP kernel) on 5.99.61 host
NetBSD wetbar.hitl.washington.edu 5.99.61 NetBSD 5.99.61 (GENERIC) #1: Sat Jan
28 13:57:59 PST 2012
Because LFS allocates metadata, specifically inode blocks, on an as-needed
basis rather than pre-allocating them the way FFS does, it estimates how much
of the rest of the disk *would* be filled with inode blocks, segment headers,
and other metadata if usage continues the same as it has for the disk thus far,
compared to the number of data blocks.
If the proportion of inode blocks is extreme---as it is for the t_renamerace
test---the filesystem can report "full" even when there is almost nothing
actually stored on the disk.
Fix the crashy part of t_renamerace (see kern/43582), and then run
Use nonlinear mixing of the actual metadata use with the projection. When the
disk is empty, the sample size that generates the projection is small, and we
should avoid reporting disk full; but when the disk approaches capacity, the
projection is more accurate (assuming a uniform pattern of use) and it is more
important to avoid reporting free space erroneously.
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