[CentOS] RAID help

Tue Dec 14 19:23:37 UTC 2010
Ryan Wagoner <rswagoner at gmail.com>

On Tue, Dec 14, 2010 at 2:08 PM, Jason T. Slack-Moehrle
<slackmoehrle at me.com> wrote:
> Hi Mark,
>
> Thanks for the reply.
>
>>> 2. Create a RAID 1 out of that partition and use a mount point of /boot
>>
>> Only if you want to mirror the boot partition.
>
> Doesn't one want to mirror that partition?

Yes you want to mirror boot. Otherwise if one drive fails you won't be
able to boot from the other drive. Also make sure you install grub on
both drives.

>
>>>
>>> 3. Create other mount points I might want i.e swap, /home, etc
>>> 4. Create RAID1 out of these partitions
>>
>> Only if you want each directory RAIDed. DO NOT mirror swap. Bad idea.
>> <snip>
>
> Right, I get that, but what is fuzzy is it you, say have a drive with a few partitions that you don't mirror and a few that you do, doesn't the drive you are mirroring to have unused space equal to the amount of the partitions you are not mirroring?

I think you are over complicating this. If you just want / in one
partition or want to use LVM to split / then do the following.

Partition both drives like

sd[ab]1 100M for boot
sd[ab]2 Fill entire space
sd[ab]3 2GB for swap

Create three mdadm RAID 1 mirrors

md0 sd[ab]1 /boot
md1 sd[ab]2 / OR LVM PV
md2 sd[ab]3 swap

If you want your data separate you can use LVM to carve out the space.
Or make one more mdadm mirror for your data.

I do know that RHEL 6 creates boot by default as larger than 100M so
you might want to determine the size to feature proof your setup.

Ryan