[PlanetCCRMA] RAID questions...kernel patch?

Fernando Lopez-Lezcano nando@ccrma.Stanford.EDU
Tue May 17 15:51:01 2005

On Tue, 2005-05-17 at 13:26, Aaron Trumm wrote:
> Hey there - have a question...
> With the current planet kernel/FC3, is SATA hardware raid supported?
> my task is to rebuild a media server to make it perform better and be solid,
> and I'm thinking of trying an FC3/planet kernel setup.  But the key part i'm
> struggling with understanding is whether I can set up the RAID mirror
> properly...
> The mobo is an ASUS p4p800se and it has two drives, which of course, we want
> to act like one, be mirrored, for safety, all that good stuff...  our
> current version of the server uses gentoo and can't take advantage of the
> ASUS hardware raid, but we're thinking we might be better off using the
> hardware raid than a software raid...
> I've read a couple places that I may need to patch the kernel - which is why
> I ask here, because the other goal is to improve its performance, and I
> don't think the current server even has any realtime patches, it's just a
> straight 2.4 kernel.  so I was thinking about just doing a mostly planet
> style install...
> anybody have any clues?  *turns eyes at fernando...*  *grin*

*fernando tries (unsuccessfully) to walk away from the virtual room*

The kernel does not have anything extra (in terms of outside patches)
and I don't know which hardware raid devices it may support. Most of the
mobo level raid devices are just software raid, they need a special
driver on windows (which, surprise, does the raid thing :-) But again, I
don't know which ones may be exceptions to that rule. 

When I set up raid (raid5) on my servers I ended up using software raid
after all. I have multiple disk (expensive) sata cards that can do
hardware raid but that ended up being slower than using a properly
configured software raid5 solution - I imagine that the limited amount
of onboard cache of the controller works against raid5 performance when
you compare it to using the whole memory space of a linux system as a
cache for writing (again, I have only tried raid5, not raid0 or raid1). 

Another advantage of software raid is that you could move the drives to
a completely different motherboard and controller and they will still be
recognized and used as a raid array. Most probably that is not true of
hardware raid, you are locked to the internal format that that
particular controller uses. 

-- Fernando