[mythtv-users] RAID versus Drobo

Eric Robinson ryunokokoro at gmail.com
Sun Sep 9 22:55:52 UTC 2007

Michael Heironimus wrote:
> On Sun, Sep 09, 2007 at 02:52:24PM -0400, Eric Robinson wrote:
>> Andy Burns wrote:
>>> On 09/09/2007 17:15, Eric Robinson wrote:
>>>> clarify things quite a bit.  I would most definitely be doing a software
>>>> [fake] RAID-5 setup in Linux.  Some digging revealed a few links:
>>> on linux, raid with mdadm isn't fake, it's software raid.
>>> dmraid is what is referred to as fake raid.
>>> then of course there's hardware raid.
>> So what then is the difference between fake raid and software raid?
> "fakeraid" in Linux refers to an entire class of controllers. They use a
> proprietary software RAID system within the driver and a special BIOS
> that knows how to boot from that proprietary software RAID. They are
> normally advertised and sold as RAID controllers with little or no
> mention of software RAID, but aside from the Windows driver and BIOS
> they're ordinary IDE/SATA controllers. Most of the Linux drivers to
> support these proprietary RAID volumes have been reverse-engineered by
> the community.
> "Software RAID" in Linux refers to the standard kernel software RAID
> system, controlled through mdadm. It runs above the HBA drivers, not
> inside them. It can theoretically work with just about any combination
> of controllers and drives on any hardware platform, though of course
> mixing and matching vastly different devices is probably not a good
> idea. I don't think you can really boot a kernel off a software RAID
> volume, but there are plenty of documents describing how to create
> redundancy for /boot and the boot loader so that's not a significant
> problem.
> You'll find similar terminology in the BSDs, except that they've shown
> even less interest in supporting fakeraid cards as anything more than
> ordinary IDE controllers.
@Michael and Robin:
Wow, thanks for the info that clears up a whole load of haziness I had
regarding the issue.  I will certainly stay away from fakeraid
implementations.  Sounds kinda nasty, actually.

That leaves me with one question:  Is Linux kernel software RAID
(controlled through mdadm) generally fast enough to serve as the media
repository for an HD MythTV setup?
  I'll be using identical 750GB 7,200 RPM drives on Intel ICH9 based
SATA II ports.  Should I fear a bottleneck here or should I be okay?

- Eric

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