quick questions RE: Intel Integrated Server RAID and FreeBSD

[John Nielsen]

On Saturday 28 March 2009 11:17:31 pm Juri Mianovich wrote:
> The Intel S5000 PSL Server board, with "Intel Integrated Server RAID". 
> I plan on using the onboard raid for a simple boot mirror.
>
> I have two quick questions:
>
> 1. What chipset/controller is this "Intel Integrated Server RAID" and
> is it well supported in FreeBSD ?  Will sysinstall recognize it ?  Is
> there a CLI tool ofr viewing status once FreeBSD is running ?

I'm not sure about the specific controller but it looks like it should be 
supported. If you set up a mirror in the BIOS before booting sysinstall 
it will likely be recognized as ar0. Note that the individual disks will 
ALSO be visible. atacontrol / ataraid are the tools you would use to 
administer such a thing.

> 2. Is this _real_ hardware raid ?  As in, FreeBSD will know _nothing_
> about the raid and will simply see one disk (which is a mirror) ?  I am
> seeing discussion that I don't understand about how this is somehow
> software raid, but If it's all built on the board ... ?

This is software RAID. The BIOS knows enough to manipulate and boot from 
arrays, and if you use the Intel driver / software on Windows it will do 
its thing there as well. The two pieces of software use the same 
metadata, etc. so the transition is more or less seamless as long as the 
driver and related services are installed and working properly under 
Windows.

Under FreeBSD, the Intel metadata format is one of many understood and 
supported by the ataraid(4) driver, which basically just extends ata(4). 
You should be able to boot, monitor array status and make repairs using 
atacontrol and friends.

> Performance isn't a real issue since it is just a boot mirror.  I just
> want to hide the raid layer from the OS and do my raid work (rebuilds,
> etc.) through the BIOS.

I haven't used this particular board but I have used Intel RAID in the 
past and share the view that software RAID is best handled at the OS 
level and not at the driver/BIOS level. You as the administrator have a 
better idea of and more control over what is going on, plus your RAID 
format (and therefore future integrity) is not tied to one vendor (or 
line, or specific card, etc.).

FreeBSD's gmirror (geom_mirror) is an excellent tool; well-documented and 
well-integrated into the OS. It is possible to boot from gmirror volumes, 
monitor array status manually or automatically (via periodic scripts), 
etc.

The only compelling potential reasons I can think of to use the onboard 
RAID are: 1) You need to see the same volumes across multiple OS'es 
(FreeBSD and Windows for example). Windows obviously doesn't understand 
FreeBSD's gmirror, etc (but it probably doesn't understand the filesystem 
either..). Since you didn't mention Windows I don't expect this is an 
issue. 2) You want to install to an array directly from sysinstall 
without any manual prep. Since you did mention sysinstall this could be 
more relevant. Unfortunately the currently shipping installer doesn't 
offer anything in the way of creating RAID or other non-vanilla volumes. 
The most straightforward way around this is to prep the gmirror disk(s) 
before running sysinstall by booting to a rescue CD or attaching the 
disk(s) to a system currently running FreeBSD, Or you can install FreeBSD 
to the primary disk, manually create your mirror and partitions on the 
secondary disk, dump/restore everything over, switch boot order and 
insert the former primary into the array. IIRC PC-BSD supports RAID 
creation at boot time, so that might give you more options.

HTH,

JN