[linux-elitists] The desktop in your pocket

Joakim Ziegler joakim@avmaria.com
Tue Jan 27 10:32:15 PST 2004


On Tue, 2004-01-27 at 05:04, Rick Moen wrote:

> SATA and soft RAID actually amounts to _two_ issues (block device support
> vs. support for whatever form of RAID is on the drives).  The easy
> answer to the RAID question is:  Blow away whatever proprietary crud is
> present, and use the Linux md driver, instead.

This is somewhat off-topic for the thread, but probably on-topic for the
list...

I'm setting up a storage server with RAID5, 6 drives of 200GB each. I
was originally going to buy something like the Promise SuperTrak SX6000,
but people kept telling me that a) that card is crap, and b) I should
just use the md driver instead, it's cheaper to get plain IDE cards than
to get a big RAID controller, and just as fast.

Now, I can get very cheap 2-bus PCI IDE controllers (silicon image
based), so that's not a problem. But I came to realize one thing that
seems strange to me in recommending the md driver: Won't this swamp the
PCI bus? A normal 33MHz 32-bit PCI bus has a theoretical max transfer
rate of about 128 MB/sec. For a RAID controller, this isn't a problem,
you read and write your data once, normally, to what looks like a normal
device. However, when I'm writing data to a software RAID5 spanning 6
disks on normal controller cards, I have to write much, much more data
across the PCI bus.

So, will my RAID5 writes become ridiculously slow when using the md
driver?

-- 
   The Private Joakim Ziegler - Not Speaking For Anyone But Myself
    joakim@avmaria.com - http://www.avmaria.com - rdgzt@Undernet
            http://www.avmaria.com/ - http://www.fix.no/
		






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