[CentOS] RAID5 or RAID50 for database?

Sat May 24 19:30:54 UTC 2008
Linux <linuxlist at gmail.com>

On Fri, May 23, 2008 at 5:31 PM, Guy Boisvert <boisvert.guy at videotron.ca> wrote:
> Well, i respect Open Source (and your opinion) very much but your comparison
> imply that you had access to Adaptec's code!  Maybe you really had access, i
> don't know.  If it's the case, then thanks you for having shared this
> knowledge.

No need to see adaptec source code. Actively developed and widely used
open-source projects have great success over their closed-sourced
big-budgeted projects. But you are correct at one point: I do not have
right to blame any vendor without a fair comparison. However, none of
them tends to show theirs for a comparison. But again, according to
general inclination, I have a great feeling that I am right. Besides,
this is all about the philosophy of open-source. linux kernel-raid
still has my vote.

Nevertheless, closed-source firmwares are everywhere, should we become
paranoid? Maybe one day, but today, software linux kernel-raid is a
good competitor in raid world, so I think it is a good choice to be
paranoid about raid-stuff. (And of course we should, it is a cheap and
great redundancy and for both data safety and service continuety)

As an example, IBM's SAN devices are great I think. I'd used one and
loved its performance and simplicity and elasticity. No software
open-source solution can easily race with it.

> You're talking about failed disks or controller?
> With controller, easy with my backups (or backup card).  People with no
> tolerance to failing controller arrange things accordingly like i do.
> With disks, irrelevant.

This is what I'm trying to explain. Even the same vendor breaks
compatibility between different vendors and I'm still talking about
controller cards. I have to have backup cards for all configurations I
have. After using a backup card, I either have to supply a new backup
for controller card or have to transfer my configuration to a new

For external solutions, I had only managed one configuration since now
so no comment/comparison on them.

> Well, educate me (and maybe others) M8.  I learn things everyday and i like
> it.  How would you do RAID10 with 3 disks?  I know how to do it with at
> least 4, then 6 and so on.
> As for RAID-10, more below.

Do not ask me, ask linux kernel raid10 developer [2]

> Well, english is neither my native language!  As for reading, i'm not that
> bad but i may have misunderstood what you really meant.  In that case,
> please forgive me!  I didn't meant to be rude or anything.

Please accept my apologies. I think I behaved somehow rude. No need to
talk about such non-technical issued in this kind of a list :)

> I agree that the compatibility is great with software RAID.  However, there
> are some limitations at least in performance (Bus saturation, etc).
> I "tried to read" your reference (the URL you kindly provided me, thanks)
> and, quote:
> "When the top array is a RAID 0 (such as in RAID 10 and RAID 50) most
> vendors omit the "+", though RAID 5+0 is clearer."
> "RAID 1+0: mirrored sets in a striped set (minimum four disks; even number
> of disks) provides fault tolerance and improved performance but increases
> complexity. The key difference from RAID 0+1 is that RAID 1+0 creates a
> striped set from a series of mirrored drives. In a failed disk situation
> RAID 1+0 performs better because all the remaining disks continue to be
> used. The array can sustain multiple drive losses so long as no mirror loses
> both its drives."
> So they say, and correct me if i'm wrong, that RAID10 is a RAID 1 of RAID 0.
>  A mirror of stripe sets.  You said it's not that, i lost you on this one.

linux kernel raid10 is a combination of both raid0 and raid1, not sum
of them. As developer himself says in [2] So you have 3x500GB disks
and 750GB raid-volume.

[2] http://neil.brown.name/blog/20040827225440

Have a nice sunday....

P.S.: Once more, I am sorry to steal someone's thread which is about
raid5/raid50 but I am currently using raid10 in many configurations
and even after some disk failures I recovered easily. So, I can
honestly recommend raid10 over raid5(0) configurations.