[K12OSN] Raid Level Choice

Les Mikesell les at futuresource.com
Wed Dec 22 20:48:11 UTC 2004

On Wed, 2004-12-22 at 13:38, Burke Almquist wrote:

> > LVM lets you combine physical volumes so you get the same effect
> > as RAID0.
> LVM gives you the space benefits but not the speed benefits of using 
> RAID 0 since it doesn't "stripe" the data across disks. (Assuming that 
> most of your writes occur to the same partition, /home say)

I think your files have to be large enough to span across disks (i.e.
more than one cylinder) before you would see a speed benefit from
the RAID0 stripe effect.  And the benefit you get from the head on
the 2nd drive being in the right place to continue reading comes
at the cost of it not being in the right place for a file someone
else wants at the same time. I'm not sure how LVM handles the
separate devices but in general for multiuser use you want as
many independently-seeking heads as you can get because disk head
motion is the slowest computer operation. RAID tends to lock them
all together. 

  Les Mikesell
   les at futuresource.com

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