Software RAID5

[Maxim Khitrov]

On 9/21/07, Gabriel Dragffy <gabe at dragffy.com> wrote:
> Hi all
>
> Hoping to get some help setting up software RAID5. Guides on the
> internet seem to be few and far between, and official documentation
> is a little too technical. Basically I have 3 x 500GB hard drives
> which I'd like to have in a raid5 configuration, using software, root
> partition on their too would be a bonus. I'd be grateful for assistance.
>
> Best regards
>
> Gabriel

>From what I know, you're not going to be able to boot from them.
However, a simple solution to that is to get a 64+ MB USB flash drive
and put the kernel on that. Just use fdisk and bsdlabel to write the
boot blocks. As long as the kernel has all needed drivers and you
specify which root device to use (either via kernel configuration or
/etc/fstab), that should allow you to put everything else on the RAID
array. This is how I currently do full-disk encryption on my laptop
using GELI. Kernel is outside, everything else is encrypted, same idea
for RAID.

I haven't ever done software RAID in FreeBSD, so can't help you with
the practical aspects of it. But I will say that technical or not, man
pages are still the best way to learn about these things. From what I
can see, RAID 5 is done through vinum, and GEOM offers RAID 3. Someone
else here may be able to tell you which one is better to use.

It's also worth noting that with software, the performance of RAID 5
is not going to be very good. I generally advise against software RAID
5. If you want good performance and reliability using software RAID,
the best bet is RAID 10, but there the utilization is 50%. I think
that if you can afford another 500GB drive and performance is
important to you, a software RAID 10 using GEOM will perform much
better. It is also easier to recover, and you can lose two drives (not
any two, but still) without completely losing all the data.