Raid10 to Raid0 conversion

Hi,

i have 4disc RAID10 on my server and i am trying to grow it to 6 devices. As direct grow of RAID10 is unavailable so I decided to do it this way:

RAID10->RAID0->Grow RAID0 to 3 devices->RAID0(3 devices)->RAID10(6devices)

But i have problem on the first step. I have degraded my RAID10 array:

# mdadm --detail /dev/md1
/dev/md1:
        Version : 1.1
  Creation Time : Mon Sep  2 12:09:53 2013
     Raid Level : raid10
     Array Size : 1023996928 (976.56 GiB 1048.57 GB)
  Used Dev Size : 511998464 (488.28 GiB 524.29 GB)
   Raid Devices : 4
  Total Devices : 2
    Persistence : Superblock is persistent

Update Time : Sat Mar 22 13:00:25 2014
State : clean, degraded
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Layout : near=2
Chunk Size : 512K

Number Major Minor RaidDevice State
0 0 0 0 removed
1 8 17 1 active sync /dev/sdb1
2 0 0 2 removed
4 8 49 3 active sync /dev/sdd1

And want to change it to RAID0:

# mdadm /dev/md1 --grow --level=0
or:
# mdadm /dev/md1 --grow --raid-devices=2 --level=0

but the result is always the same:
mdadm: /dev/md1: could not set level to raid0

dmesg shows:
md/raid0:md1: All mirrors must be already degraded!
md: md1: raid0 would not accept array

But the array is already degraded... What am I doing wrong ?

I am using Centos 6.5 default version of kernel and mdadm.

PS: I know that it is possible to grow RAID10 by creating new array with 3 drives and 3 missing and then move data between them, but i am trying to grow live system without any offline time.

Regards,
Marcin Wanat

People here don't have that information. You'll increase your chance of getting help if you post output from "uname -a" and "mdadm -V" instead of referring to OS version.

Mikael Abrahamsson    email: [email protected]

It is available with latest kernel and mdadm...

I don't think it is you.
What does /sys/block/md1/md/degraded contain?
If it isn't '2', then that is the problem.
Maybe if you stop the array the array and assemble it again it could get that right.

uname -a ; mdadm -V

is more helpful.

NeilBrown

In fact i have resolved this issue a day later.
I saw that despite output of mdadm --detail (which was WD=RD=4), in dmesg there was: RD: 5, WD:4 so i guessed that raid array was not degraded correctly. I have fixed it by just stopping and reassembling the array as you said.

Regards,
Marcin Wanat