Re: [Xen-users] XCP on HW RAID - how to?

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

Rudi Ahlers wrote:

> I would simply disable the RAID setup in the BIOS and then configure a
> mdraid in Linux. By the sounds of it you have what's called "fakeraid"
> and will probably have more trouble trying to get Linux to see the
> drives, than trying to figure out how to setup software RAID on Linux
> :)
That's my thinking as well. As it happens I've just been 
updating/upgrading some of my boxes. One new (to me box doesn't have 
raid so that forced me to use Linux software raid. The next one I did 
is  Dell box with built in hardware raid - but I've disabled that and 
gone software raid again because it gives me more flexibility and 
visibility. Only one of the three Dell boxes I have has any Linux 
support for the raid controller AFAICT.
I'd tended to steer clear of software raid because of the problems 
booting from an array before you've loaded the software needed to 
access it. Then I came across this neat trick ...
You can setup a small boot volume as raid 0 (mirrored) - you can add 
all your drives. The trick is to run "grub-install /dev/sdx" for each 
drive. This means that every drive in the array has a copy of the 
boot loader (GRUB) and the required files (initrd, vmlinuz, etc). In 
other words, the system can be booted from any single drive - and the 
initrd has the software needed to then access everything else.
Obviously, booting off only one drive probably doesn't make sense for 
many array configurations.
Now I'm a convert. The last box I upgraded had new (larger) drives. 
It was really handy to be able to configure the raid with a drive 
missing since the supplier shipped one less than ordered. Then when 
the missing drive arrived I just added it, told mdadm to add it to 
the arrays, and let it build the data on it.

But in relation to the query. Once you have supported raid volumes, 
then what you run on top of it doesn't really matter. Ie, as far as 
XCP (or any other software) is concerned, it shouldn't matter if a 
disk partition is on a hardware raid, software raid, single disk, ...
--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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