Conventional wisdom has it that DBMSes do internal caching and are very smart about doing IO, so any caching/buffering the OS does is wasted and actually leads to worse performance.

On Linux (2.4.18, SuSE 8.1) direct access to underlying disks is done via special raw devices and some restrictions apply (RAW(8) man page):

Because raw I/O involves direct hardware access to a process's memory, a few extra restrictions must be observed. All I/Os must be correctly aligned in memory and on disk: they must start at a sector offset on disk, they must be an exact number of sectors long, and the data buffer in virtual memory must also be aligned to a multiple of the sector size. The sector size is 512 bytes for most devices.


Is raw IO supported on Linux?


--
 Regards Flemming Frandsen - http://dion.swamp.dk
 PartyTicket.Net co founder & Yet Another Perl Hacker

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