[...]
RC> The idea is that the database vendor knows their data storage
RC> better than the OS can guess it, and that knowledge allows
RC> them to implement better caching algorithms than the OS can
RC> use. The fact that benchmark results show that raw partition
RC> access is slower indicates that the databases aren't written
RC> as well as they are supposed to be.
I am not convinced that this conclusion is warranted, though I admit I
have not seen those benchmarks. The DB vendor's raw disk driver might
be doing things like synchronous writes for maintaining its own
invariants, while a [non-journalling] file system will care about fs
meta-data consistency at best. While it is possible that the general
purpose file system with more man-hours behind it is better written,
the benchmarks might be omitting crucial criteria like crash
protection and such. Do you guys have references to benchmarking
data?
RC> ... One of
RC> which was someone who did tests with IBM's HPFS386 file system
RC> for server versions of OS/2. He tried using 2M of cache with
RC> HPFS386 and 16M of physical cache in a caching hard drive
RC> controller and using 18M of HPFS386 cache with no cache on the
RC> controller. The results were surprisingly close on real-world
RC> tests such as compiling large projects. It seemed that 2M of
RC> cache was enough to cache directory entries and other
RC> file-system meta-data and cache apart from that worked on a
RC> LRU basis anyway.
This I would buy, as you point out the controller and the FS code
are doing the same thing (if they are giving the same write guarantees).
BM
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