Re: wish for Linux MD mirrored raid types

["Keld Jørn Simonsen" <keld@keldix.com>]

On Fri, May 06, 2011 at 12:34:36PM -0300, Roberto Spadim wrote:
> 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?


I think more complex -> more intelligent, more features.

I think it is actually amazing what raid10 can do.
Is raid 1 in other systems really limited to say 2 disks
- mirrored? Then linux raid10 is much more intelligent. 
> 
> check others raid system (freebsd, netbsd) and check how they do...

Yes, and also HW raid. If Linux made raid10,far the default for RAID1,
then I think Linux would compare very well with other operating systems
and HW raid.

Best regards
keld

----

> 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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