RAID Cards

Mark Bucciarelli mark at
Fri Jul 1 19:27:53 GMT 2005

On Thu, Jun 30, 2005 at 04:34:13PM -0500, Dan Nelson wrote:
> In the last episode (Jun 30), Mark Bucciarelli said:
> >
> > I don't see the big win in hardware raid.
> The three big plusses for hardware raid are: if you get one with
> battery-backed cache (strongly recommended), then the array can cache raid-5
> writes until it gets full stripes, and can hold off doing mirror writes if
> there are pending read requests.  

Ah ... this is certainly a win for an io-bound system.

> Also, if your power goes out or the system spontaneously reboots, you won't
> have to rebuild parity or resync the mirrors (assuming battery-backed
> cache).  

We pay a lot of money to ensure the lights stay on and sacrifice small animals
to avoid spontaneous reboots.

> And finally, hardware raid cards will automatically rebuild onto a hot spare

I know I could do this with Linux software raid, not sure about gmirror.

> if available and you can swap out the dead drive and swap a new spare in
> without having to run a single command.

Another win.  Thanks, your brought up some issues I hadn't thought of.

I expect hardware raid cards will go the way of modems and printers and
offload their processing to the main CPU.  And I guess the choice partly
depends on whose software you trust more--free software from FreeBSD or
proprietary code written in a cathedral.  You can probabaly guess my bias.  ;)


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