Matthias Buelow wrote:
Chuck Swiger wrote:
PS: Haven't we had this conversation before?
Yes, indeed, and I don't want to reopen that issue since that would
lead to no new insights (and since I don't have the time atm. to
contribute anything I couldn't provide any stuff myself).
Yet you seem willing to spend time discussing the matter...?
I was just refuting the claim of "very robust" filesystem when power goes
out in the context of 200GB consumer-grade hardware that this thread
was talking about.
Most of the time, a FreeBSD system will come back up without losing data older
than about thirty seconds, and that is tunable. Have you even tried to change
the syncer sysctls I mentioned?
I think until a satisfactory solution can be
found (by making softupdates and/or a journalled filesystem as
reliable as possible through mechanisms like write-request barriers
and appropriate flushing at these) users who're running FreeBSD on
end-consumer hardware (desktop PC as workstation or personal server)
should be warned that softupdates does NOT work as described on
their hardware and that the filesystem can easily be corrupted when
the power goes out, no matter if softupdates is enabled or not.
Great. I think "man ata" already says exactly this:
hw.ata.wc
set to 1 to enable Write Caching, 0 to disable (default is enabled).
WARNING: can cause data loss on power failures.
If your hard drive no longer works correctly when write-caching is disabled,
it's defective. Nothing FreeBSD or any other system can do is going to change
that.
One often sees the "softupdates" argument being fielded by FreeBSD
advocates, typically against Linux users with journalled fs, on web
forums, usenet and other less authoritative (and knowledgable)
places of discussion, and it is often presented as if it were some
kind of magic bullet that makes filesystem corruption impossible.
"Often?" Strawman test: can you point out 3 examples by message-id or URL?
And if you prefer to run a journalled filesystem under Linux instead of
softupdates under FreeBSD, by all means, do whatever makes you happy.
This simply is not so.
Very good.
--
-Chuck
PS: I don't want a thread to end on a negative note. It would be useful if
FreeBSD had a more adaptable method for dealing with drive power management and
caching; in particular, for laptops it might be nice to cache data for much
longer-- perhaps even hours-- if nothing fsync()s, in order to permit the drive
to spin down.
(This is something both Windows and MacOS X are learning to do pretty well.)
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