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Re: Cheapest "software" RAID card

On Tue, Oct 25, 2005 at 01:28:11PM +0800, Jason Lim wrote:
> > >I've had no issue using Sarge's Debian Installer to install to
> > >Silicon Image SATA controllers.
> As I mentioned, it can be detected, BUT there is no RAID function. That
> is, it can detect the individual HDs connected to the SIL card, but it
> cannot use the RAID function at all, even if it is setup on the SIL card's

It's not clear why you would ever want to use the RAID function,

Are you saying though that if you configure a single logical drive
in the card's RAID BIOS, then the Debian Installer can't see this
drive at all?

> One of the main points is that the SIL cards and others support Hotplug
> (well, not all models do) while many on-board controllers do NOT support
> hotplug.

To have reliable hotplug with SATA you need not only a controller
which supports it, but also a backplane and drives - normal SATA
drives do not support hotplug, nor do the normal SATA connectors.

If you are spending money on backplane and drives then I see no
reason not to spend money also on a decent hardware RAID card that
supports hotplug such as 3Ware.

Without backplane and drive support I wouldn't like to try hotplug
unless the drive was already seen as dead by the system and had been
removed from any arrays, all of which you can do with Linux md.

> Also, I found that many times, if a HD connected to the
> motherboard failed, then the system would crash or stall, while if the HD
> is connected to one of these "cheap" RAID cards, at least the system would
> continue to function.

Well, this is still not an argument for using the fake RAID of the
controller, since any such hotplug protection the controller is
giving should apply whether you have it configured to present a RAID
device or JBOD, yes?

> So these cheap RAID cards do have their function if performance is not
> your highest goal.

They have their function as SATA controllers I would not argue
there, I just question the value of their RAID support.

> I guess right now the only option is to use a Silicon Image card (or
> whatever) and then use md on top of that, but as I said, it would be much
> more graceful if the Kernel supported the RAID card's implementation (like
> it does with 3ware, or Megaraid, or the more expensive ones), OR if md
> could somehow tie into the RAID card's system... or read the RAID card's
> BIOS to get the config.

Yes it would be nice if every RAID-aware controller would hook into
Linux's md (or allow the reverse), especially because many people
don't trust md's auto-assembly yet without it you need an initrd if
your root filesystem is on an md filesystem.  If the card could tell
the kernel what to assemble then that makes things simpler.

I'm sure from the vendor's point of view though that there are many
reasons why not to bother doing/allowing this, and in the meantime
we have md which in most respects is better than the "fake hardware
RAID" the vendors provide.

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