[CentOS] mdraid Q on c6...

Sun Jun 22 12:38:50 UTC 2014
Ljubomir Ljubojevic <centos at plnet.rs>

On 06/22/2014 02:28 PM, Ljubomir Ljubojevic wrote:
> On 06/22/2014 10:15 AM, John R Pierce wrote:
>> so, I installed a c6 system offsite today, had to do it in a hurry.
>> box has 2 disks meant to be mirrored...  I couldn't figure out how to
>> get anaconda to build a LVM root on a mirror, so I ended up just
>> installing a /boot and vg_system on sda and raid it later.
>> every howto I find for linux says to half-raid the OTHER disk, COPY
>> everything to it, then boot from it and wipe the first disk and then
>> bond it as a mirror of the 2nd.   Thats kind of ugly.
>> in solaris, you can tell it that your existing partition is half of a
>> mirror, update /etc/vfstab, then reboot, and then join a mirror to it.
>> this seems much cleaner to me than copying everything.
>> I tried to do this the solaris way, and at the first step, am told...
>>       # mdadm --create /dev/md0 --level=mirror --raid-devices=2 /dev/sda2
>>       missing
>>       mdadm: cannot open /dev/sda2: Device or resource busy
>> /dev/sda2 contains the LVM root vg...
>> so... I'm thinking I''ll boot a rescue system from usb, create the half
>> mirror, then reboot to the incomplete raid and add mirror /dev/sdb2
>> will the VG be found on /dev/md0 instead of on /dev/sda2 ?
>> if so, is there any other reason this won't work?
> This is a best RAID tutorial I saw so far, and I made it better and
> safer (commands by just copying will fail due to /dev/sdx naming):
> https://www.facebook.com/notes/centos/software-raid-on-rhel-6/10151254589767728

If you create just a RAID1 then you can get away with 1 failed device. I 
do not think RAID10 will be accepted with just one device + one failed.

There might be option to just change the type of partition on existing 
HDD and write metadata with mdraid command, joining it to some existing 
raid device, but I never tried it and I would not attempt it on 
important hdd's.

And here are commands for fast partition + RAID1 + RAID10 creation:


Ljubomir Ljubojevic
(Love is in the Air)
PL Computers
Serbia, Europe

StarOS, Mikrotik and CentOS/RHEL/Linux consultant