[geeks] RAID0+1 and ideas, etc...

[Phil Stracchino]

On 11/07/13 11:12, Jonathan Katz wrote:
> All,
> 
> Say you're running a Linux server. It has six Fusion IO cards, each
> presents two disk devices giving you a total of 12 disk devices. You
> want to RAID 1+0 this setup so that if any physical card or disk
> device dies, you're still operational.
> 
> My customer set this up using mdraid to stripe the two disk devices
> within the individual cards. So we go from 12 disk devices to six md
> stripes. Then the md stripes are mirrored card-by-card (so there are 3
> md mirror/RAID1 devices.) Then LVM is used to stripe the three
> remaining cards into one large volume that we use.
> 
> I'm not sure this is the best way to do it, and I want to hear from
> others who deal with this what they think (which is why I'm throwing
> this out there.) The requirement is for one decent sized, reliable
> storage pool of data. I think we have an extra layer of abstraction
> here, but I'm not sure how to redo this, or if we even should.
> 
> What say the mind trust?


This seems ...  really overly complex.  It sounds like a case of
throwing money at the problem without actually thinking it through
first.  Even without FusionIO's advice not to mirror FusionIO cards.

If I were doing this, I'd mirror the devices in such a way that no two
submirrors of the same mirror are on the same card, then stripe all the
mirrors together.  Either that, or configure the FusionIO cards to
present a single volume each, if possible, and RAID10 them normally.
Configuring the cards to present two devices each only to stripe them
together in software just seems completely irrational unless there's no
way to make them present a single device.


-- 
  Phil Stracchino
  Babylon Communications
  phils at caerllewys.net
  phil at co.ordinate.org
  Landline: 603.293.8485