> YES! I recently discovered that VirtualBox apparently defaults to > ignoring flushes, which would, if true, introduce a failure mode > generally absent from real hardware (and eventually resulting in > consistency problems quite unexpected to the user who carefully > configured her journaled filesystem or transactional RDBMS!)
I recommend everyone to be extremely hesitant to assume that any particular storage setup actually honors write barriers and cache flushes. This is a recommendation I would give even when you purchase non-cheap battery backed hardware RAID controllers (I won't mention any names or details to avoid bashing as I'm sure it's not specific to the particular vendor I had problems with most recently). You need the underlying device to do the right thing, the driver to do the right thing, the operating system in general to do the right thing (which includes the file system, block device layer if any etc - for example, if use md on Linux with RAID5/6 you're toast). So again I cannot stress enough - do not assume things behave in a non-broken fashion with respect to write barriers and flushes. I can't speak to expensive integrated hardware solutions; I HOPE, though at this point my level of paranoid does not allow me to assume, that if you buy boxed systems from companies like Sun/HP/etc you get decent stuff. But I can definitely say that paying non-trivial amounts of money for hardware is not a guarantee that you won't get completely broken behavior. <speculation> I think it boils down to the fact that 99% of customers that aren't doing integration of the individual components in overall packages, probably don't care/understand/bother with it, so as long as the benchmarks say it's "fast", they sell. </speculation> -- / Peter Schuller PGP userID: 0xE9758B7D or 'Peter Schuller <peter.schul...@infidyne.com>' Key retrieval: Send an E-Mail to getpgp...@scode.org E-Mail: peter.schul...@infidyne.com Web: http://www.scode.org
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