IO Subsystems / RAID Controller
Types of RAID Controllers
In general there are two types of RAID controllers out there: The ones with
battery backed write cache and the ones without it. The later ones cost less but
are much slower on write oerations.
There is one controller that has a redundant battery backed cache and that is
the only controller caching log writes (email me for the brand and model - I try
to keep the site ad free).
RAID Controller Cache Settings
SQL Server is very good in caching the right data in memory and reading ahead if
it thinks that it is going to need more data, so in general it does not make
sense to use read cache on RAID controllers.
If your RAID controller has a battery backed write cache and lets you choose how
to configure the ratio between read and write cache I recommend that you use
100% write cache.
If your RAID controller has no battery backed write cache you sould test if
disabling the write cache does make your system read faster from disk. Since SQL
Server is very unlikely to read data from the disk twice the RAID controller can
skip the time he needs to transfer the data into the read cache