[CentOS] software raid

Thu Mar 29 19:13:33 UTC 2007
John R Pierce <pierce at hogranch.com>

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?  

> c)  12TB RAID0 w/no redundancy =>  $0.32/GB
> When my scratch data increases in importance, I'll have to investigate 
> that new fangled RAID 6 thang.  :)  Does RAID6 suffer from this 
> performance degradation bogey man when used with ext3?  Isn't RAID6 
> just RAID5 with a redundant parity stripe across 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 

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.