Re: 3ware vs. MegaRAID

Scott Carey wrote:
> * Change the linux 'readahead' block device parameter to at least 4MB (8192, see blockdev --setra) -- I don't know if
thereis a FreeBSD equivalent. 
>
I haven't tested them, but 3ware gives suggestions at
http://www.3ware.com/kb/Article.aspx?id=14852 for tuning their cards
properly under FreeBSD.  You cannot get good sequential read performance
from 3ware's cards without doing something about this at the OS level;
the read-ahead on the card itself is minimal and certainly a bottleneck.

As for your comments about drives being faster at the front than the
end, the zcav tool that comes with bonnie++ is a good way to plot that
out, rather than having to split partitions up and do a bunch of manual
testing.

--
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us