mdadm RAID 1+0 setup question

[Mr. B-o-B]

I have a new server with 4 disks that I want to setup as a RAID 1+0 setup.

I was curious what is the best practice for this setup.

I have seen some howto's about setting up RAID 1+0 where they just use one
array for everything.

My gut is telling me I should create at a minimum

RAID 1 (all 4 disks) /swap
RAID 1 (all 4 disks) /boot
RAID 1+0 (all 4 disks) /

Is my gut correct in telling me I should play it safe with the /swap &
/boot as there own RAID 1's?

Any advice would be greatly appreciated.

Thanks!

Mr. B-o-B

[+Alan Hicks+]

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On 2012-05-15, Mr. B-o-B <mr.che...@gmail.com> wrote:
> RAID 1 (all 4 disks) /swap
>

> Is my gut correct in telling me I should play it safe with the /swap &
> /boot as there own RAID 1's?

Nope, your gut is entirely wrong there for swap. Much better would be
to setup four smaller swap partitions, one on each disk. This will use
less space, provide more swap, and improve performance because the
kernel can write to the least active swap partition should you get to
the point of using swap.

- --
It is better to hear the rebuke of the wise,
Than for a man to hear the song of fools.
Ecclesiastes 7:5
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[Mr. B-o-B]

+Alan Hicks+ cried from the depths of the abyss...

>> RAID 1 (all 4 disks) /swap
>>
>> Is my gut correct in telling me I should play it safe with the /swap &
>> /boot as there own RAID 1's?
>
> Nope, your gut is entirely wrong there for swap. Much better would be
> to setup four smaller swap partitions, one on each disk. This will use
> less space, provide more swap, and improve performance because the
> kernel can write to the least active swap partition should you get to
> the point of using swap.

Indeed. That make a lot of sense. I think I was in "Over Thinking Mode"
when I sent this post. Thanks for the advice.

[Douglas Mayne]

On Fri, 18 May 2012 02:28:41 +0000, +Alan Hicks+ wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 2012-05-15, Mr. B-o-B <mr.che...@gmail.com> wrote:
>> RAID 1 (all 4 disks) /swap
>>
>> Is my gut correct in telling me I should play it safe with the /swap &
>> /boot as there own RAID 1's?
>
> Nope, your gut is entirely wrong there for swap. Much better would be to
> setup four smaller swap partitions, one on each disk. This will use less
> space, provide more swap, and improve performance because the kernel can
> write to the least active swap partition should you get to the point of
> using swap.
>

I am wondering if there shouldn't be a middle ground approach between the
two approaches. If something is swapped out by the kernel it assumes it
can be able to "get it back." A two disk RAID 1 doubles the odds of being
able to do that. A setup that mirrors the same area of swap four times
might be overkill, but having no redundancy when a random disk error
occurs could lead to the affected application failing, and that might
even be the kernel itself. The compromise would create 2 swap partitions
on raid 1 mirrors spread across 4 drives. Anyway, that's my 2 cents.

--
Douglas Mayne