[mythtv-users] Linux software raid question

Gerald Brandt gbr at majentis.com
Thu Jun 5 12:31:32 UTC 2008


I've been running a 5x250 software raid5 array for a few years. It's easy to setup and maintain and uses very little CPU. If I had the cash, I'd prob convert to hardware raid5, and buy 2 controllers (1 spare). 

Sadly, I don't have the cash, so my biggest decision now is: when I build a new system, do I go software raid 5 or software raid 6? 

Gerald 

----- "Dan Ritter" wrote: 
> On Wed, Jun 04, 2008 at 07:27:16PM -0400, Carl L. Gilbert wrote: 
> > On Wed, 2008-06-04 at 15:04 -0400, Dan Ritter wrote: 
> > > On Wed, Jun 04, 2008 at 02:49:11PM -0400, Carl L. Gilbert wrote: 
> > > > Hardware RAID does not have to be expensive. 
> > > 
> > > Of course it does. Let's say that software RAID takes up 1% of 
> > > your CPU. 1% of a $200 CPU is $2. There are no reliable hardware 
> > > RAID systems that cost $2. 
> > > 
> > Your forgot to include a percentage of the cost of the drive's 
> > interface. Yes, most interfaces do this today, but still. Since you 
> > want to be technical, that cost is based in your motherboard. 
> 
> I don't know any general-purpose motherboards that don't have disk 
> controllers these days, but let's suppose that you need to stock 
> some generic SATA-PCI controllers. $10 buys a nice reliable one 
> built on a Silicon Image chip. 
> 
> > > If the card blows, you had better have a replacement on hand of 
> > > exactly the same type. Not so for software RAID. And if the card 
> > > blows after warranty or after the manufacturer has EOL'd it, you 
> > > might be looking at a very expensive replacement. 
> > > 
> > Hardware is hardware. If your drive controller blows it blows. Don't 
> > matter if its on the MB or in a card plugged into the MB. No difference 
> > here. 
> 
> Except, of course, that a RAID controller is a much more 
> expensive card to keep stocked. Often more expensive than 
> complete motherboards. Sometimes more expensive than complete 
> motherboards, CPUs, and RAM. 
> 
> > I am not claiming HW does something software does not. You are claiming 
> > the superiority of what I assume is FakeRAID. 
> 
> No, I'm claiming that superiority, in many circumstances, of 
> Linux Software RAID, done through generic disk controllers and 
> controlled via mdadm. 
> 
> > So what do you do when one of your drives dies on software RAID? Put in 
> > a new drive and go about your business? Nope. Since you are not 
> > RAIDing drives but partitions. So you have to rebuild your partition 
> > table on the new drive. I don't know how thats done, but for me, 
> > putting in a new drive and switching on the computer is very simple. 
> 
> # sfdisk -d /dev/good_disk |sfdisk /dev/new_disk 
> 
> > > > runs smartmon no problem. Plus there is a web interface to manage the 
> > > > drives from within the OS. 
> > > 
> > > That's not an advantage. 
> > > 
> > I am claiming only 1 advantage of HW raid, Its simpler. 
> 
> I'm done trying to convince you. 
> 
> -dsr- 
> 
> 
> -- 
> http://tao.merseine.nu/~dsr/eula.html is hereby incorporated by reference. 
> 
> When freedom gets lots of exercise, it protects itself. 
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> 

-- 
Gerald Brandt 
Majentis Technologies 
204-229-6595 
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