mdadm, raid10, and problem

mdadm, raid10, and problem

[Maciej 'Agaran' Pijanka]

Hello


i was trying to build raid 10 from six devices (currently loops but need
to check before i try to do same on physical drives).

and mdadm gets bit mad, 

mdadm -C -l10 -n6 /dev/loop1 /dev/loop2 /dev/loop3 missing missing
missing
produced weird result 

when tried loop missing loop missing loop missing it worked

i understand that its logical to give three pairs of devices but
content of error wasn't logical in any way

mdadm 2.6

[root@develbox /]# mdadm --create  /dev/md0 -l10 -n6 -R /dev/loop0 /dev/loop1 /dev/loop2  missing missing missing
mdadm: /dev/loop0 appears to be part of a raid array:
level=raid10 devices=6 ctime=Sun May 20 17:32:43 2007
mdadm: /dev/loop1 appears to be part of a raid array:
level=raid10 devices=6 ctime=Sun May 20 17:32:43 2007
mdadm: /dev/loop2 appears to be part of a raid array:
level=raid10 devices=6 ctime=Sun May 20 17:32:43 2007
mdadm: RUN_ARRAY failed: Input/output error
mdadm: stopped /dev/md0
[root@develbox /]#

-from dmesg:
md: bind<loop0>
md: bind<loop1>
md: bind<loop2>
md: md0: raid array is not clean -- starting background reconstruction
raid10: not enough operational mirrors for md0
md: pers->run() failed ...
md: md0 stopped.
md: unbind<loop2>
md: export_rdev(loop2)
md: unbind<loop1>
md: export_rdev(loop1)
md: unbind<loop0>
md: export_rdev(loop0)
[root@develbox /]#


ps. am not subscribed, please cc to me

best regards
maciej pijanka


-- 
agaran at pld dash linux dot org :: PLD Linux Developer [#133161]
I do not fear computers. I fear the lack of them. [Isaac Asimov]

Re: mdadm, raid10, and problem

[Neil Brown]

On Sunday May 20, agaran@pld-linux.org wrote:
> 
> Hello
> 
> 
> i was trying to build raid 10 from six devices (currently loops but need
> to check before i try to do same on physical drives).
> 
> and mdadm gets bit mad, 
> 
> mdadm -C -l10 -n6 /dev/loop1 /dev/loop2 /dev/loop3 missing missing
> missing
> produced weird result 

What did you expect :-?

> mdadm: RUN_ARRAY failed: Input/output error
> mdadm: stopped /dev/md0

Yes, lots of mdadm's errors are - like this - quite unhelpful.  It is
something that I would like to get improved, but it just doesn't get a
high priority.

> -from dmesg:
> md: bind<loop0>
> md: bind<loop1>
> md: bind<loop2>
> md: md0: raid array is not clean -- starting background reconstruction
> raid10: not enough operational mirrors for md0

"not enough" means "you don't have the right drives".

For every level other than raid10, it doesn't matter which drives you
have, it just matter how many there are.
For raid10, you do that to have are set of drives that provides all
blocks.  But I just re-used the error message from raid1.

Patches always welcome...

NeilBrown