RAID-3?

[Greg 'groggy' Lehey]

On Thursday, 19 August 2004 at  8:33:58 +0200, Poul-Henning Kamp wrote:
> In message <20040819062228.GO85432 at wantadilla.lemis.com>, "Greg 'groggy' Lehey"
>  writes:
>> On Thursday, 19 August 2004 at  0:00:55 -0600, Scott Long wrote:
>>>
>>> I think that you're really reading far too much into this.
>>
>> That depends on whether you care about accurate terminology or not.
>> Or maybe it's you who is reading too much into the matter.
>
> I think being accurate is a great thing, but accuracy of definition
> should never get in the way of working code.

Agreed.  I don't think it is.

> The main features of RAID3 are the always full stripe access which
> keeps your disk heads running in tandem which has desirable
> performance characteristica.

... for single accessors.

But a single IDE drive nowadays can transfer 40 MB a second.  A 5 disk
RAID-3 array should thus be able to transfer 160 MB a second.  What do
you need that for?

> Also the fact that you can trivially add ECC instead of mere parity
> is a big plus.

Ah, but that would be RAID-2.  Or something similar.

> Raid5 with two bit ECC (sometimes called raid6)

I thought RAID-6 was RAID-5 with two identical parity disks.  Not so?

> is a royal nightmare to code (see the raidframe paper)

Does this define RAID-6, or just describe the pain?

> whereas RAID3 in 4+2 or 8+3 is pretty trivial because of the
> full-stripe access pattern.

Sure, easy coding is good.  And having written a RAID-5
implementation, I can believe what a nightmare that an ECC version
might provide.

> Now, can we stop the definition-thumbing and let Pawel work on his
> code ?  If need be, put this on your bumper-sticker:
>
> 	If you don't like RAID3 then don't use it!

No, I think that's too simplistic.  I don't see anybody stopping Pawel
from doing what he wants.  It would be nice to know why, though.

Greg
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