[mythtv-users] Linux software raid question

Carl L. Gilbert clg-social at rigidsoftware.com
Wed Jun 4 23:27:16 UTC 2008

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.

> > This is an incredibly biased opinion. "Large drawbacks"??  Come on.  You
> > can transfer RAID arrays between computers by moving the card with them.
> > Very easy. Just as easy as software.
> 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

> (I have had both these problems occur.)
> > My 3ware RAID runs smartmonitor on it daily.  Completely smart
> > monitorable.
> > I also get an email if there is a problem.
> Ditto software RAID. 
I am not claiming HW does something software does not.  You are claiming
the superiority of what I assume is FakeRAID.

> > > When one adds in the cost of hardware RAID, and any potential upgrades
> > > like battery backed RAM caches, I would much rather put that money
> > > toward a server quality motherboard with ECC RAM, a largish UPS unit
> > > and set up RAID drives with write-intent bitmaps[3] and do weekly data
> > > check sweeps[1] via cron combined with smartmon short and long disk
> > > checks[2] on a daily and weekly basis.  Most of the features of the
> > > high end harware RAID cards are now part of the feature set of Linux
> > > soft RAID, it really is that good.
> > 
> > I don't know why you are down on hardware RAID, but its not as you
> > describe it and I dont see any advantage of software RAID.  It takes
> > more jumping through hoops.  Especially to boot on RAID.  Maybe things
> > are better now.
> > 
> > I think HW is just simpler.
> Then you'd be wrong. 
> Hardware RAID has its place, certainly. But main CPUs get
> faster and cheaper, faster than specialized CPUs on RAID controllers.
> When I build a cluster for my company, the web servers use
> software RAID mirroring, and the database servers get expensive
> hardware RAID controllers.

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.

> > 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.

> -dsr-

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