Stupid RAID question

[Alejandro Imass]

On Mon, Oct 3, 2011 at 3:55 PM, Andrej Marjan <andrej-igvx78u1SeH3fQ9qLvQP4Q at public.gmane.org> wrote:
> I've been having rotten luck with reliability of 1TB drives, so I'm finally
> biting the bullet and trying to figure out RAID. So far I have a tenuous,
> but (seemingly) working grasp of how to make device mapper do RAID1 and how
> to make it play nice with grub and LVM.
>
> My question: is it possible to do a new install into a sort of "degraded"
> RAID1 setup with only a single drive, and then add the second drive later,
> or do I need to wait until I acquire the second drive before installing?
>

It depends. It's usual, and actually quite typical to have the OS and
boot system in a non-RAID drive and then start your array from that
disk. For example, older servers had a boot-up IDE drive and then from
there you would start the array.

You have to differentiate software and hardware raids. There are some
cheap motherboards out there that actually support some RAID over SATA
but usually very limited to RAID 0 or RAID 1, and sometimes level 5.
Anyway, for most applications level 5 is overkill and you need to have
many drives for it to be really effective. I honestly wouldn't use
cheap SATA RAID controllers as these usually require a software
component as well and are really not as reliable as true hardware RAID
(e.g. 3com).

For usual street hardware (off-the-shelf SATA MBs) software RAID 10
(1+ 0 nested) is the best cost/effective and fault tolerant solution I
have worked with, on cheap hardware. It only requires 4 drives for the
array and tolerates one drive failure on each side. I usually use a
separate boot drive in any case and is usually a good idea.

So my recommendation use 3 or 5 drives:

1 small boot drive and then 2 others in raid 1, or 4 in raid 10

Best,

-- 
Alejandro Imass









> Thanks,
>
> Andrej
>
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