Subject: Re: comparing raid-like filesystems
To: Jason R Thorpe <firstname.lastname@example.org>
From: Greg 'groggy' Lehey <email@example.com>
Date: 02/01/2003 13:10:45
On Friday, 31 January 2003 at 18:17:30 -0800, Jason R Thorpe wrote:
> On Sat, Feb 01, 2003 at 12:35:45PM +1030, Greg 'groggy' Lehey wrote:
>> On Friday, 31 January 2003 at 14:18:12 -0500, Greg A. Woods wrote:
>>> [ On Friday, January 31, 2003 at 10:32:22 (-0800), Jeremy C. Reed wrote: ]
>>>> Subject: comparing raid-like filesystems (was Re: Experimental support forATA "RAID" volumes)
>>>> On Thu, 30 Jan 2003, Jason R Thorpe wrote:
>>>>> I would actually prefer to see a much lighter-weight RAID implementation
>>>>> in NetBSD.
>>>> Does one exist?
>>> No freely available RAID implementation that is "much lighter-weight"
>>> than RAIDframe exists, at least not so far as I can discover.
>> I suppose it depends on what you mean by "lighter-weight". If you're
>> talking about CPU load, I don't think that any of the implementations
>> add much to it.
> I'm mostly referring to:
> * RAIDframe's code size. It's huge. It's gigantic.
Hmm. So it is. I could 42,000 lines of code, compared to 12,000 for
Vinum. As somebody else observed, that includes full volume manager
> * RAIDframe's over-zealous use of threads. It makes multiple
> context switches for each component I/O. That's .. pathetic.
Vinum doesn't do any context switches except for some recovery
> * RAIDframe's twisty-maze of data structures. Eek.
Can't claim that Vinum is better until I look at them more carefully,
but you've just scared me off.
> * RAIDframe's multiple-implementations-of-some-things (like
> N-way XOR), some synchronous, some asynchronous (so much
> for adding hardware acceleration for computation of parity
> blocks when in non-degraded mode).
> Let's face it, we can do better. RAID card vendors put RAID 0,1,5
> implementations into reasonably small amounts of flash every day ..
> I mean, the firmware updates fit easily onto a floppy with lots of
> room to spare. And then they proceed to run that firmware on i960s,
> which aren't the fastest CPUs around.
One of the things on my tuit queue is to port Vinum to NetBSD or
OpenBSD. I even have somebody in India who wants to do it "as an
exercise to learn kernel programming". If anybody else is interested,
we could give it a try.
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