Re: The old raw devices chestnut.

Jim Smith <jim_at_jimsmith.demon.co.uk> wrote in news:dS4PuczgskeAFwJq_at_jimsmith.demon.co.uk:

> Sybase: (some experience)
> Sybase claim filesystems are faster, because of OS buffering, but
> unsafe for the same reason. They only ever suggest filesystem for
> tempdb. They don't seem to have heard of fsync()[1]

Your data on Sybase ASE is dated. Sybase allows you to use buffered devices and you can elect to have the writes posted (DSYNC=on) or buffered (DSYNC=off). Sybase has always recommended one uses raw devices.

For all DB's, I always use raw devices based on the benchmark numbers I've run and intuitively, it makes sense. If you have a read-mostly table, you may gain from utilizing OS buffering with a 32-bit DB and more than 4G of main memory on the box. (I'm over simplifying however not too much).

A benchmarking trick I learned from one of the team members was to use symlinks to my raw devices. If I needed to add more disks to a particular volume, I could down the DBMS, dd the data out to another disk, rebuild the volume, dd the data back, start the DBMS. Voila!

Regards,

-- 
Pablo Sanchez - Blueoak Database Engineering, Inc
http://www.blueoakdb.com