Re: [gentoo-user] Xen with Gentoo as dom0: sw or hw raid?

[J. Roeleveld]

On Wednesday, July 20, 2016 06:13:36 PM Jarry wrote:
> Hi Gentoo-users,
> 
> I'm going to build a small server with Xen-hypervisor with
> Gentoo as dom0 (if it is possible). Comming from ESXi-world,
> there is no choice (only true hw-raid is supported).
> 
> But what about Linux? What's preffered way to go? Software-raid
> (mdadm), or true hardware raid-controller? I have a few spares
> (LSI-9271), these worked quite well with ESXi but I'm not sure
> they are supported by Linux at all, and if there is actually
> some way of monitoring controller-health...

LSI is generally quite well supported with Linux.
See: https://www.thomas-krenn.com/en/wiki/Smartmontools_with_MegaRAID_Controller

This indicates that LSI cards also provide SMART-data of the disks itself via 
smartmontools.

> Concerning sw-raid, I have used it for quite some time, but
> never with Xen (is it actually possible?).

Yes, it is possible. But the reason why software raid can be faster on bare 
metal, might no longer be true when using Xen best practices.
Dedicating a limited amount of cores to the dom0 also means that you have less 
cores available for the software raid part.

> Moreover, grub-config
> for Xen itself is somehow more complicated and sw-raid could add
> extra complexity...

Using Grub1:
---
title Xen
root (hd0,1)
kernel /xen.gz dom0_mem=4GB,max:4G console=vga dom0_max_vcpus=1 dom0_vcpus_pin
module /kernel-4.1.7-hardened-r1-host softlevel=xen
---

I compile in the initramfs and commandline these days.
But if using a seperate one, simply add an extra "module" line:

---
title Xen
root (hd0,1)
kernel /xen.gz dom0_mem=4GB,max:4G console=vga dom0_max_vcpus=1 dom0_vcpus_pin
module /kernel-3.16.5-gentoo dolvm root=/dev/vg/root rootfstype=ext4
module /initramfs-genkernel-x86_64-3.16.5-gentoo
---

> So the question is simple. For Xen-server with Gentoo as dom0,
> what do you recommend: sofware- or hardware-raid?
> 
> Any other general tips concerning Xen (particularly with Gentoo
> as dom0)?

No specific Gentoo-tips, it's actually quite well supported.

If you prefer an appliance-like dom0, you could also look into XenServer. 
There is a free-to-use version available. Downside: the graphical management 
client is MS Windows only.

--
Joost

Re: [gentoo-user] Xen with Gentoo as dom0: sw or hw raid?

[J. Roeleveld]

On Sunday, July 24, 2016 02:48:41 PM R0b0t1 wrote:
> I would strongly suggest softraid. And qemu.

Few requests here:
1) LEARN to quote properly
2) Learn to provide reasons why.

Neither suggestions make sense.

--
Joost

Re: [gentoo-user] Xen with Gentoo as dom0: sw or hw raid?

[R0b0t1]

I would strongly suggest softraid. And qemu.

Re: [gentoo-user] Xen with Gentoo as dom0: sw or hw raid?

[J. Roeleveld]

On July 20, 2016 6:13:36 PM GMT+02:00, Jarry  wrote:
>Hi Gentoo-users,
>
>I'm going to build a small server with Xen-hypervisor with
>Gentoo as dom0 (if it is possible). Comming from ESXi-world,
>there is no choice (only true hw-raid is supported).
>
>But what about Linux? What's preffered way to go? Software-raid
>(mdadm), or true hardware raid-controller? I have a few spares
>(LSI-9271), these worked quite well with ESXi but I'm not sure
>they are supported by Linux at all, and if there is actually
>some way of monitoring controller-health...
>
>Concerning sw-raid, I have used it for quite some time, but
>never with Xen (is it actually possible?). Moreover, grub-config
>for Xen itself is somehow more complicated and sw-raid could add
>extra complexity...
>
>So the question is simple. For Xen-server with Gentoo as dom0,
>what do you recommend: sofware- or hardware-raid?
>
>Any other general tips concerning Xen (particularly with Gentoo
>as dom0)?
>
>Jarry

Short answer: if Linux kernel supports it. It will work inside the dom0.

Whatever is best depends in your requirements as linux sw raid can perform 
better that hw raid.
But. For Xen ensure you dedicate at least 1 core exclusively to dom0. Don't 
have any of your guests (domU) access the same CPU core as your dom0 uses.

As for grub complexity. I don't find this difficult. And even using UEFI boot 
for Xen isn't too difficult.
This is based on using either grub1 or EFI. Not using grub2 on any of my Xen 
machines.

--
Joost
-- 
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