I'm wondering if there's the optimal Cache setting for the following Raid controllers and raid setups. (OS: windows 2008 R2, App: II7, DB: SQL Server 2008 R2 Enterprise)

PERC 6/i:

(The default setting seems to be: No Read Ahead/Write-back)

2 Disks Raid 1 contains OS, IIS installation as web host

PERC H700:

2 Disks Raid 1 contains OS, SQL Server installation and Transaction logs

4 Disks Raid 10 contains only SQL Data file

What would be the optimal cache setting for the above three Raid configs with respect to their usage?


Yes (usually); assuming BBWC/FBWC your cache settings should match your R/W ratio.

Write-back should only be enabled if you have BBWC/FBWC. If your writes are particularly sensitive (usually not with journaled writes) then you should only use write-through.

If you're contiguous reads are commonly larger than the block size (sequentially reading large files) then you should enable read ahead. If your reads are most commonly small random IO, then it should be disabled.

All of this is highly dependent on your particular application and data. If you have no idea, you probably need to profile the IO subsystem. However, if performance isn't currently an issue, I wouldn't spend much time on it.

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