[mythtv-users] Linux software raid question

Dan Ritter dsr-myth at tao.merseine.nu
Wed Jun 4 19:04:55 UTC 2008

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.

> 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.

(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. 

> > 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.

> runs smartmon no problem.  Plus there is a web interface to manage the
> drives from within the OS.

That's not an advantage.


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