Re: LVM over RAID, or plain disks? A:"Yes" = best of both worlds?

[Neil Brown <neilb@suse.de>]

On Mon, 29 Nov 2010 23:00:19 +0700 hansbkk@gmail.com wrote:

> 2010/11/29 Keld Jørn Simonsen <keld@keldix.com>:
> >> I can see how RAID6 is simpler than RAID10, but compared to RAID1?
> >
> > Hmm, does not compute by me. RAID1 and RAID10 are the same in complexity,
> > RAID10 is just a modern RAID1, and should actually have been called
> > RAID1.
> 
> My understanding is that if I use RAID10 on a single pair of disks
> then that is literally the same as RAID1. These to me are very simple
> in that I can take either one of the pair and mount it on any normal
> machine and get at the data without doing anything special.
> 
> However, if I have my six disks configured as a single RAID10 array, I
> believe this is no longer true - the data from (at least the larger
> of) the files has been distributed over all six disks, correct?
> 
> Now compare putting LVM on top of this array, compared to three RAID1
> pairs on the one hand and a RAID6 array on the other (third) hand :)
> 
> If I were trying to recover the data using the latest version of a
> LiveCD - say Fedora or Knoppix, which would be easier?
> 
> I'm not trying to score any points, it's a genuine question.


If you are comparing recovering after some sort of problem with
a RAID10 over 6 devices compared with  LVM over 2 2-device RAID1s, then the
former is certainly easier.  This is simply because there are less layers of
complexity where something could go wrong.

In both cases, your data will be spread across multiple disks, and any one
disk or even any two disks would be of no use to you.

NeilBrown

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