Re: What's the typical RAID10 setup?

[David Brown <david@westcontrol.com>]

On 04/02/2011 14:53, Keld Jørn Simonsen wrote:
> On Fri, Feb 04, 2011 at 12:34:00PM +0100, David Brown wrote:
>> On 04/02/2011 09:27, Stan Hoeppner wrote:
>>> Keld Jørn Simonsen put forth on 2/4/2011 1:06 AM:
>>>
>>>> Well RAID1+0 is not the best combination available. I would argue that
>>>> raid10,f2 is significantly better in a number of areas.
>>>
>>> I'd guess Linux software RAID would be lucky to have 1% of RAID deployments
>>> worldwide--very lucky.  The other 99%+ are HBA RAID or SAN/NAS
>>> "appliances" most
>>> often using custom embedded RTOS with the RAID code written in assembler,
>>> especially in the case of the HBAs.  For everything not Linux mdraid, RAID
>>> 10
>>> (aka 1+0) is king of the hill, and has been for 15 years+
>>>
>>
>> I wonder what sort of market penetration small cheap SAN/NAS
>> "appliances" have these days, aimed at the home markets and small
>> offices.  These are almost invariably Linux md raid devices, although
>> the user views them as an black-box appliance.
>>
>> However, though they use md raid, they typically don't support RAID10,
>> RAID1+0, RAID10,f2, or anything other than RAID0, RAID1 and RAID5.
>
> I wonder why this is so. (I cannot dispute what you are saying, as I have
> not got any experience with any small SAN/NAS devices).
>
> Anyway, Linux NAS/SAN devices should run a kernel that should be able to
> run MD raid10 and RAID 1+0 - as this has been in the Linux kernel
> for more than 5 years.
>

I think it is just a matter of simplifying the interface for the 
expected use of the target audience.  The typical customer of such NAS 
appliances doesn't know enough about raid to understand the detailed 
pros and cons of different types, and is unlikely to care about small 
performance differences.  Thus they have the options of raid0 and JBD 
for maximal space per $, raid1 for two disks with redundancy, and raid5 
for more disks with redundancy.  They don't have hot spares, raid6, 
mixing raid levels on different partitions, etc.  Keep it simple, and 
people can use it.

Of course, you can always access these devices directly, or with ssh, 
and re-arrange things as you want.  It's only the web-based user 
interface that is limited.

> For c0mpanies that sell Linux NAS/SAN devices, I would have thought that
> they would have at least one engineer following this list.
> Maybe they will not disclose themselves, but are there some of you out
> here?
>
> And what kind of support of RAID types are available on your box?
>
> And maybe the more advanced stuff is available, but only in some CLI.
> The configuration web server could be without the more advanced oprions.
> But then: why not use options that kind of doubles the performance
> compared to competitors?
>
> Are the raid 1+0 and md raid10 options available via some ssh
> or other CLI access mechanisms? I know on routers, there are
> normally a CLI interface.
>
> Furthermore, Linux has a good penetration in the server market.
> And I think most people would run servers with raids, if they do
> something serious. So Linux RAID should be more than 1 %, at least
> in the server market.
>

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