Re: [tlug] SATA software RAID or SAS hardware RAID?

[Al Hoang <hoanga@example.com>]

Hi Peter,

On Sat, Dec 09, 2006 at 01:04:34PM +0900, Peter Van der Weeen wrote:
> [snip] 
> Options are:
> (1)   2 x SATA II 250GB disks with software RAID-1 
> (2)   SAS5iR controller + 2 x 300GB SAS (10k) disks and hardware RAID-1
> 
> Option (2) costs about 100.000 yen more than (1) 
[snip]
> We don't need to go for the latest and the greatest, I simply want something
> that gives us as much performance as possible at a reasonable cost.
> 

	If you're not looking for the latest and greatest then in terms
of performance you don't sound like you're hurting too much or perhaps you
are?  While disk access definitely does matter in a web/db server setup
one question I'm not sure on is whether you're running into performance
issues with your current setup.  And how much different the new hardware
setup will be from your current setup.
	If you have done benchmarking and profiling of your setup 
(long, tedious and ultimately the final answer on most things performance)
and find you need all the disk speed acess you can get then it makes sense
to plop down more money on a real hardware RAID controller as this an
offload system load to the RAID controller and perhaps get a decent benefit.
But it seems from a quick read that this also matters on how well the
RAID controller drivers will work with Linux.   This is something that might
need some research as a poorly supported hardware RAID controller under
Linux will be a big disappointment. So you might want to look at this checklist
and prioritize to help you identify whether options (1) or (2) are better:

*. Price
*. Disk access read speed  (RAID-1 tends to be better)
*. Disk access write speed (RAID-1 should not be faster than only one disk)
*. CPU load
*. Ease of maintenance (Which one do you know better?)
*. Driver support (Do you want to spend the next weekend trying to patch
   the next kernel revision in order to get your RAID controller working?)
*. Price (People keep bringing this up all the time :-)  so I add it in again)
	
	Here's some more references to help you make a decision...

The Waikato LUG has setup a very nice wiki collecting people's
experiences on software and hardware RAID:
http://www.wlug.org.nz/SoftwareRaidVsHardwareRaid
A quick thread on the SAS5iR controller card (Seems to indicate this driver
requires a binary driver)
http://www.archivesat.com/Linux_on_Dell_PowerEdge_Servers/thread2194835.htm
Someone else went through the long and tedious process of benchmarking 
Hardware RAID and software RAID (Note this is an old setup)
http://www.chemistry.wustl.edu/~gelb/castle_raid.html

Alain