Re: managing raid on Linux

[Bill Davidsen <davidsen@tmr.com>]

David Lethe wrote:
> -----Original Message-----
> From: Keld Jørn Simonsen [mailto:keld@dkuug.dk] 
> Sent: Wednesday, April 23, 2008 1:47 PM
> To: David Lethe
> Cc: Ty! Boyack; linux-raid@vger.kernel.org
> Subject: Re: managing raid on Linux
>
> On Wed, Apr 23, 2008 at 01:17:19PM -0500, David Lethe wrote:
>   
>>    Well, this is the norm. While some APIs are well done, the other
>> extreme is that vendor xyz farmed out the API/drivers to another
>> company, and the hardware vendor doesn't have the resources, knowledge
>> or experience to provide the information necessary to bring a 3rd-party
>> management tool to market.   I will certainly not reveal anything about
>> the companies that did farm out the software/firmware to 3rd parties,
>> and will not tell you if their names were mentioned in this post.
>> Suffice to say that this is a real problem with SOME controllers that
>> people reading this post have installed in their computers.
>>
>>   - The economics of developing support for a particular controller is a
>> severe constraint.  Consider the reasons above, and then add simple
>> equipment costs for development/testing, and then support.  I'm not
>> going to add support for product xyz unless I know it will be
>> profitable, and even a hundred end-user requests won't begin to pay for
>> such an effort.
>>
>>   - I for one certainly can't keep up with all the new things coming
>> out, so we choose our battles wisely based on the market opportunity,
>> longevity of the controller platform, safety/robustness of the API, and
>> development/ongoing support expense.
>>
>> So there are the reasons why the OP can't find anything that supports
>> everything he has.
>>     
>
> David, thanks for your explanation of the current situation for making
> an übermanageri for HW RAID. The prospects seem dark indeed. 
>
>   
If there were an ubermanager then products could compete on only price 
and performance. Now they can compete on ease of use as well, and that's 
not all bad for the customer. Corporations try to skimp on system 
management (usually) and often ease of use is the differerce between 
mediocre management and totally incompetent.

> Are there then more future in doing it the SW RAID way, as the Linux
> Kernel stuff we are discussion here on this mailing list?
>
>   
The advantage is in the portability, you need not spend the top dollar 
on hardware to get quite good results.

> Are there chances that this work om Linux RAID can match or be better
> on the issues of performance, raid personality flavours and management,
> compared to the best of the HW RAID manufacturers? 
>
>   
No, not the best. The reason is that Raid-N, where N>0, writes recovery 
information, either mirrors or CRCs, or similar. Software raid must pass 
this as multiple writes, opening a chance for consistency problems, and 
always taking more bus bandwidth. So better than the best dedicated 
hardware it is not, and can't be. As good as the "very good" hardware 
solutions, yes. More flexible to expanding with whatever hardware is 
cost effective when you need it, SW raid wins every time.

-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark 



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