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

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Subject: Re: [Xen-users] XCP on HW RAID - how to?
From: Stanislav Datskevich <me@xxxxxxxxxxxxxxx>
Date: Fri, 08 Jul 2011 12:53:25 +0400
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Hi. I'm using HW RAID too (but LSI 3ware 9750) and want to install XCP 1.0 on it. I think it will be much faster than mdraid.
Can I integrate driver to the distro somehow?

07.07.2011 13:20, Simon Hobson:
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, ...

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