[CentOS] RAID5 or RAID50 for database?

Fri May 23 14:31:45 UTC 2008
Guy Boisvert <boisvert.guy at videotron.ca>

Linux wrote:
> On Fri, May 23, 2008 at 8:28 AM, Guy Boisvert <boisvert.guy at videotron.ca> wrote:
>> "More intelligently designed" -> Could you please tell us more on this one?
> Simple answer: Open Source (and for a long time) I guess you know what
> it means. But I wander if source of Adaptec raid controller's firmware
> is opened in recent years.

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.

>> Not easily recoverable?  I did recovery many time without a hitch (Adaptec,
>> 3Ware, LSI, PERC)!
> Try recovering 3Ware failed disks with Adaptec then. Nearly every
> vendor has his own way in details. Yes, mostly documented but not
> interchangable. And I do not mean only RAID-1.

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.

>> As for RAID 10 with 3 disks, mmm... go see:
>> http://en.wikipedia.org/wiki/Redundant_array_of_independent_disks
> mdadm Raid-10 is neither 1+0 nor 0+1. So 3 disks is enough to supply a
> minimum level of redundancy. You should have 2 copies of each stripes
> on either 2 of 3 disks. But in 3 disk configuration loss of 2 disk
> means total loss. Go check with man mdadm.

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.

> Well, my parents taught me understanding what I read better than you
> (although I'm not a native English speaker)

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.

>> Hey, have a nice day "Linuxito" !
> Thanks buddy.
> And for referance, try reading this [1]
> I do not want to start a flame, just sharing my experience with
> different hardwares. This comparison about software-hardware raid
> excludes SAN and other external RAID solutions. Externally attached
> storage is outside the scope of this discussion. Externally connected
> solutions can obviously be SAN, software RAID, hardware RAID, or a
> combination thereof. [1]
> [1] http://linux.yyz.us/why-software-raid.html

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.

    |-- Mirror ----|
    |              |

   -- D1a        -- D1b
   |             |
   | Striped     | Striped
   |             |
   -- D2a        -- D2b
   |             |
   ...           ...
   |             |
   -- Dna        -- Dnb

So that's why i don't get what you mean by RAID10 with 3 disks.  Please 

Guy Boisvert, ing.
IngTegration inc.