On Fri, 19 Nov 2010, Roberto Nunnari wrote:

> Could you please tell me how to tell grub and initrd to mount read-only
> half of a raid1 set, please?

If you've got sda1 and sdb1 making up md0, then just mount sda1/sdb1 ro.

jh
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On 11/19/2010 04:32 AM, Roberto Nunnari wrote:
>> 1. http://wiki.alteeve.com/files/an-cluster/ks/generic_server_rhel6.ks
>
> Thank you for your reply.
>
> Does that kickstart effectly produces a partitioning that is
> exactly the same on both disks? Because that is the problem
> I'm facing: the partitioning produced by the kickstart
> is different on the two drives.

Yup, both disks are identical layout.

> Also, why did you put /boot and swap in raid? Was it for
> obtaining identical partitioning on both drives?
> For swap, the kernel already does performance optimization
> when swap partitions are on different drives, and /boot..
> I always tended to keep /boot be as simple as possible, to avoid
> any problem during boot.. but maybe, these days with initramdisk
> there's no more need for that..
>
> Best regards.
> Robi

Keeping the drives identical is a big part of it. Even on my 3+ disk
RAID level 5 systems, I make /boot a RAID 1 mirrored across all drives
as /boot can not be RAID5.

I mirror /boot and <swap> because if either is lost, the system dies.
Imagine if something was in swap, then swap vanished, and then the
system tried to retrieve what was in swap... Not so good. :P

The biggest concern is that, on /boot, you need to ensure that grub has
been setup on all drive's MBR. The grub shell allows you to ensure that.

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Digimer ha scritto:
> On 11/19/2010 04:32 AM, Roberto Nunnari wrote:
>>> 1. http://wiki.alteeve.com/files/an-cluster/ks/generic_server_rhel6.ks
>>
>> Thank you for your reply.
>>
>> Does that kickstart effectly produces a partitioning that is
>> exactly the same on both disks? Because that is the problem
>> I'm facing: the partitioning produced by the kickstart
>> is different on the two drives.
>
> Yup, both disks are identical layout.
>
>> Also, why did you put /boot and swap in raid? Was it for
>> obtaining identical partitioning on both drives?
>> For swap, the kernel already does performance optimization
>> when swap partitions are on different drives, and /boot..
>> I always tended to keep /boot be as simple as possible, to avoid
>> any problem during boot.. but maybe, these days with initramdisk
>> there's no more need for that..
>>
>> Best regards.
>> Robi
>
> Keeping the drives identical is a big part of it. Even on my 3+ disk
> RAID level 5 systems, I make /boot a RAID 1 mirrored across all drives
> as /boot can not be RAID5.
>
> I mirror /boot and <swap> because if either is lost, the system dies.
> Imagine if something was in swap, then swap vanished, and then the
> system tried to retrieve what was in swap... Not so good. :P
>
> The biggest concern is that, on /boot, you need to ensure that grub has
> been setup on all drive's MBR. The grub shell allows you to ensure that.
>

Thank you for the explanation. Now I have a good reason for swap
to be in raid1.

Best regards.
Robi
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On Nov 19, 2010, at 10:17 AM, Digimer <linux@alteeve.com> wrote:

> I mirror /boot and <swap> because if either is lost, the system dies.
> Imagine if something was in swap, then swap vanished, and then the
> system tried to retrieve what was in swap... Not so good. :P

You could use LVM to create LV for swap and root. Performs the same, plus you can resize them. Just make the PV the RAID set after /boot.

-Ross

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On 11/19/2010 07:18 PM, Ross Walker wrote:
> On Nov 19, 2010, at 10:17 AM, Digimer<linux@alteeve.com> wrote:
>
>> I mirror /boot and<swap> because if either is lost, the system dies.
>> Imagine if something was in swap, then swap vanished, and then the
>> system tried to retrieve what was in swap... Not so good. :P
>
> You could use LVM to create LV for swap and root. Performs the same, plus you can resize them. Just make the PV the RAID set after /boot.
>
> -Ross

This is true. I wasn't, mainly, because I was using the remainder of the
free space on the disks, post install, to create a DRBD device which
clustered LVM sat on. Thought stacked LVM work, it pushed too far into
"corner case" territory for my comfort level.

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