build out of a server advice

Lloyd Brown lloyd_brown at byu.edu
Mon Jun 25 09:24:32 MDT 2012


I would add that there are effective capacity differences between the
different RAID levels.  For example, for N disks of K size:

RAID5:
total capacity = (N-1)*K

RAID6:
total capacity = (N-2)*K

RAID10:
total capacity = N*K/2


Depending on your application, it's possible that, like you say "Disk is
cheap", and that's enough to minimize the impact of capacity issue for
the OP.  But I think it's wise to present all the details, and let him
decide what's important for the application, budget, etc.

I certainly like it when vendor reps, etc., do that for me.

Lloyd Brown
Systems Administrator
Fulton Supercomputing Lab
Brigham Young University
http://marylou.byu.edu

On 06/23/2012 10:27 AM, Nicholas Leippe wrote:
> Raid6:
> - can withstand any combination of double disk fault
> - much worse healthy write performance than 1+0
> - huge performance penalty in degraded and rebuild mode
> 
> Raid1+0:
> - can only withstand specific combinations of double disk fault (must
> not be two pairs of the same mirror)
> - minimal healthy write performance penalty
> - performance hardly affected in degraded mode, rebuild mode is a
> simple copy--no CPU calculations, just I/O


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