RAID Cards performance issue

[Scott Balneaves]

On Mon, Dec 08, 2008 at 08:21:38AM +0800, Christopher Chan wrote:

> Software raid5 get performance penalties but a hardware raid card with 
> sufficient cache memory (must be battery backed if you want to minimize 
> data loss) and processing power can do raid5 and perform as well as or 
> even better than raid10 depending on the number of drives involved.

No, RAID5's a compromise.  If it's a compromise in software on the server,
it'll be just as much of a compromise on a dedicated controller, where
it'll be implemented in software running on the card's controller.
I've run tests myself on 3Ware controllers, and they are MUCH slower in
a RAID5 config than either a RAID1 or RAID10 config.  This isn't a smack
at 3ware controllers: I use them myself, and they're great.  Solid, dependable
raid controllers.  It's just a limitation of RAID5.  RAID5 tries to be
everything to everybody ("More Space!!" "Fault Tolerant!!" "Less Filling!!")
and in the end, doesn't really satisfy anyone.

> RAID0? The guy has lost one drive already and you tell him RAID0 as a 
> choice for performance? Even if I don't care about the data, I would not 
> want to go through the trouble of replacing and recreating the array 
> everytime a disk decides it does not want to play anymore.

Sorry, I meant RAID1 not RAID0.

Cheers,
Scott

-- 
Scott L. Balneaves | Perilous to all of us are the devices of an art
Systems Department | deeper than we ourselves possess.
Legal Aid Manitoba |    -- Gandalf [J.R.R. Tolkien, "Lord of the Rings"]