Re: wish for Linux MD mirrored raid types

[Roberto Spadim <roberto@spadim.com.br>]

hum, i asked this question one time, the point is:
raid1 code is very easy
raid10 code is more complex

easy = faster, less memory, less cpu
complex = faster?, more memory? more cpu?

check others raid system (freebsd, netbsd) and check how they do...

2011/5/6 Keld Jørn Simonsen <keld@keldix.com>:
> On Fri, May 06, 2011 at 10:01:48AM -0400, Miles Fidelman wrote:
>> Keld Jørn Simonsen wrote:
>> >>As you say, RAID10,near on four disks is pretty much identical to
>> >>RAID1+0 - i.e., a stripe of two normal RAID1 pairs.
>> >>
>>
>> I don't that's exactly right.  At least as I understand it:
>>
>> - RAID1+0 (and RAID0+1) nests things - you start with two sets of RAID1
>> mirrors, then stripe across them (or vice versa) - it's a nested set of
>> steps
>>
>> - md RAID10 provides both mirroring and striping, but it's a more
>> integrated function - (from the man page) "RAID10 provides a combination
>> of RAID1 and RAID0, and sometimes known as RAID1+0. Every datablock is
>> duplicated some number of times, and the resulting collection of
>> datablocks are distributed over multiple drives." - but there isn't an
>> inherent nesting in the process (i.e., no two disks are copies of each
>> other, and md RAID10 will work over odd numbers of drives)
>
> Yes, you are right, RAID1+0 is nested, while Linux MD raid10 is not.
> But the data layout of Linux MD RAID1+0 and Linux MD
> RAID10,near is almost identical.
>
> keld
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-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
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