On Linux Filesystems - Mailing list pgsql-performance

Bruce Momjian commented:

 "Uh, the ext2 developers say it isn't 100% reliable" ... "I mentioned
 it while I was visiting Red Hat, and they didn't refute it."

1.  Nobody has gone through any formal proofs, and there are few
systems _anywhere_ that are 100% reliable.  NASA has occasionally lost
spacecraft to software bugs, so nobody will be making such rash claims
about ext2.

2.  Several projects have taken on the task of introducing journalled
filesystems, most notably ext3 (sponsored by RHAT via Stephen Tweedy)
and ReiserFS (oft sponsored by SuSE).  (I leave off JFS/XFS since they
existed long before they had any relationship with Linux.)

Participants in such projects certainly have interest in presenting
the notion that they provide improved reliability over ext2.

3.  There is no "apologist" for ext2 that will either (stupidly and
futilely) claim it to be flawless.  Nor is there substantial interest
in improving it; the sort people that would be interested in that sort
of thing are working on the other FSes.

This also means that there's no one interested in going into the
guaranteed-to-be-unsung effort involved in trying to prove ext2 to be
"formally reliable."

4.  It would be silly to minimize the impact of commercial interest.
RHAT has been paying for the development of a would-be ext2 successor.
For them to refute your comments wouldn't be in their interests.

Note that these are "warm and fuzzy" comments, the whole lot.  The
80-some thousand lines of code involved in ext2, ext3, reiserfs, and
jfs are no more amenable to absolute mathematical proof of reliability
than the corresponding BSD FFS code.

6. Such efforts would be futile, anyways.  Disks are mechanical
devices, and, as such, suffer from substantial reliability issues
irrespective of the reliability of the software.  I have lost sleep on
too many occasions due to failures of:
 a) Disk drives,
 b) Disk controllers [the worst Oracle failure I encountered resulted
    from this], and
 c) OS memory management.

I used ReiserFS back in its "bleeding edge" days, and find myself a
lot more worried about losing data to flakey disk controllers.

It frankly seems insulting to focus on ext2 in this way when:

 a) There aren't _hard_ conclusions to point to, just soft ones;

 b) The reasons for you hearing vaguely negative things about ext2
    are much more likely political than they are technical.

I wish there were more "hard and fast" conclusions to draw, to be able
to conclusively say that one or another Linux filesystem was
unambiguously preferable for use with PostgreSQL.  There are not
conclusive metrics, either in terms of speed or of some notion of
"reliability."  I'd expect ReiserFS to be the poorest choice, and for
XFS to be the best, but I only have fuzzy reasons, as opposed to
metrics.

The absence of measurable metrics of the sort is _NOT_ a proof that
(say) FreeBSD is conclusively preferable, whatever your own
preferences (I'll try to avoid characterizing it as "prejudices," as
that would be unkind) may be.  That would represent a quite separate
debate, and one that doesn't belong here, certainly not on a thread
where the underlying question was "Which Linux FS is preferred?"

If the OSDB TPC-like benchmarks can get "packaged" up well enough to
easily run and rerun them, there's hope of getting better answers,
perhaps even including performance metrics for *BSD.  That, not
Linux-baiting, is the answer...
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