[mythtv-users] Linux software raid question

Dan Ritter dsr-myth at tao.merseine.nu
Thu Jun 5 10:34:53 UTC 2008

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.


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