[rescue] Small RAID array setup

C. Magnus Hedemark chris at yonderway.com
Thu Jun 26 13:29:03 CDT 2003

On Thursday, June 26, 2003, at 01:07 PM, Sheldon T. Hall wrote:

> I would prefer security, capacity, and speed, in that order, for the 
> setup.

RAID 1 is going to give you the greatest security, but the worst 
capacity.  RAID 1 is not an option with more than 2 drives.  RAID 0+1 
or RAID 10 (distinct technical difference but no real practical 
difference) have the same 50% available capacity, the same resiliance 
as RAID 1, and better performance.

You need an even number of drives to do RAID 1, RAID 0+1, or RAID 10.  
The fifth drive would be a paperweight unless called into duty as a 
spare when one drive failed.

RAID 5 is less secure (you can only stand to lose one drive in the 
array) but gives you much more capacity.  In your case, 80% of the 
space would be usable and the remaining 20% would be used for parity.  
Read performance would be fine but write operations will be slow.  
Especially if you do software RAID instead of hardware RAID.  You need 
to determine how much writing you do to figure out if you can live with 
the performance.

Many "sysadmin mill"-papered sysadmins will just use RAID 5 without 
considering the consequences.  If you're running an ftp site where you 
get lots of downloads but few uploads, RAID 5 is likely fine.  If you 
are running a file server that does lots of writing, you may find it a 
bit slow.


C. Magnus Hedemark
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