[CentOS] software raid

Thu Mar 29 19:30:41 UTC 2007
Joshua Baker-LePain <jlb17 at duke.edu>

On Thu, 29 Mar 2007 at 12:13pm, John R Pierce wrote

> chrism at imntv.com wrote:
>> Joshua Baker-LePain wrote:
>>> You know, the whole "disk is cheap, so why use RAID5?" argument just 
>>> doesn't wash with me.  Sure, disk *is* cheap.  But some of us need every 
>>> GB we can get for our money (well, given I'm spending grant money, it's 
>>> actually *your* money too (if you live in the US)).
>>> To demonstrate, let's look at a 24 drive system (3ware has a 24 port 9650 
>>> board).  Newegg has 500GB WD RE2 drives for $160.  So for $3840 in drives 
>>> I can get:
>>> a) 6TB RAID10 => $0.64/GB
>>> or
>>> b) 10.5TB RAID6 w/ hot spare => $0.37/GB
>>> Umm, I'll take 75% more space for the same money, TYVM.
> did those prices factor in the drive bay infrastructure for 24 drives with 
> cabling, redundant power supplies, etc?

Given 3840=160*24, no.  ;)  But those prices would be the same however you 
configure the drives.

> btw, I would NOT build a 20-something raid5/6 set.  the rebuild times would 
> be massively slow, opening a large window for double drive failure. 
> Before you say 'nah, would never happen', check out phpbb.com, they lost 
> their web server and forums to a double failure last month, and yes, they had 
> a hotspare so the rebuild started immediately.
> The large SAN vendors usually don't recommend building raid5 sets larger than 
> 6-8 disks, and will stripe or concatenate multiple of those on the typical 
> SAN with 100s of spindles.    Myself, I'll stick with RAID10 for anything 
> critical.

Would that I had the money to and still get the space I need.  Even doing 
2 12 disk RAID6 sets (each with a hot spare) gets you 9TB which is 50% 
more space for the same money as RAID10.

To try to cut this debate short (hah!), this all boils down to a simple 
CBA.  For me, I need massive amounts of fairly reliable, fairly fast space 
at as good a price as I can manage.  RAID5/6 on systems backed up to tape 
(oops, I seem to be crossing threads) fulfills those requirements.  For 
me.  YMMV.  No guarantees.  Offer not valid in NV or NY.  Do not taunt 
Happy Fun Ball(TM).

Joshua Baker-LePain
Department of Biomedical Engineering
Duke University