Re: Software RAID, a bit OT

[Seth Mos <knuffie@xxxxxxxxx>]

At 07:38 18-7-2002 -0400, Danny Cox wrote:
>         Since you say you're on a budget, I'd say look for a different
> (cheaper) IDE controller.  In the hardware benchmarks (take all
> benchmarks with a large grain of salt, of course) I've seen, ATA-133
> buys you little at the present time, even IF the drive supports it.  The
> drives just aren't that fast yet.

I have had no real problems with the promise ata controllers. The fastrak 
raid controllers are a different story however. Other choices of ide 
controllers are the Highpoint or CMD controllers.

>         So, look for another controller, and go for the extra disk.

I have a software raid 5 which has disks on a promise ata66 controller and 
no problems so far.
I know they didn't and don't have really good driver support but the 
standard controllers seem to work right now.

>         The problem with XFS and RAID5 has to do with XFS writing in multiple
> block sizes, and how Linux RAID5 implements that.  Steve has been
> working on it, and has made it better, but there's still more to do.
> It's better, but by how much, I can't say.

It's better and you can notice the difference. It's still nu up to par with 
"normal" disk access though. The recent changes that went in for smaller 
blocksize support and the alignment support for EVMS means that it is 
getting "close to completion"*.

* Completion is a non existant term in a software development project and 
should be handled as such.

>         Given that, pop for the extra disk, and implement a RAID 0+1.  It
> should be a bit faster than RAID5, I think.

Much faster then raid 5 but that is more by design then the other issues. 
Raid 5 has parity overhead and raid 10 has not. Read speeds of a raid 5 and 
a raid 10 should be rather close. The big difference is the write speed you 
can obtain.

>         As others have noted, the 3ware controllers have been getting lots of
> praise on this list.

4 80GB disks of about ?120,- = ?480,-
1 3ware 7450 OEM = ?600,-

Getting a 3ware controller would mean more then doubling the price of your 
raid setup.
You could get the 7410 if you are doing raid 10 which is ?430,- but that 
would mean you can buy 4 more disks for the price of a single controller.

Cheers

--
Seth
It might just be your lucky day, if you only knew.