Mark Mielke wrote:
Is there anything in POSIX that seems to suggest this? :-) (i.e. why
are you going under the assumption that the answer is yes - did you
read something?)
It was something somewhere on the Sun web site, relating to tuning Solaris
filesystems. Or databases. Or ZFS. :-(
Needless to say I can't find a search string that finds it now. I
remember being surprised
though, since I wasn't aware of it either.
I don't believe POSIX has any restriction such as you describe - or if
it does, and I don't know about it, then most UNIX file systems (if
not most file systems on any platform) are not POSIX compliant.
That, I can believe.
Linux itself, even without NCQ, might choose to reorder the writes. If
you use ext2, the pressure to push pages out is based upon last used
time rather than last write time. It can choose to push out pages at
any time, and it's only every 5 seconds or so the the system task
(bdflush?) tries to force out all dirty file system pages. NCQ
exaggerates the situation, but I believe the issue pre-exists NCQ or
the SCSI equivalent of years past.
Indeed there do seem to be issues with Linux and fsync. Its one of
things I'm trying to get a
handle on as well - the relationship between fsync and flushes of
controller and/or disk caches.
The rest of your email relies on the premise that POSIX enforces such
a thing, or that systems are POSIX compliant. :-)
True. I'm hoping someone (Jignesh?) will be prompted to remember.
It may have been something in a blog related to ZFS vs other
filesystems, but so far I'm coming
up empty in google. doesn't feel like something I imagined though.
James
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