Growing a RAID 1+0 configuration

nibbiodagliocchiali · 06-02-2008, 09:03 AM

Hi

I'd like to assemble a home file server based on Kubuntu with software RAID (using mdadm command)

Operating system on disk (/boot, /var, /home, /swap and so on..)

/dev/sda

Storage space, formatted with XFS filesystem, composed by a RAID 1+0 as follows
(here I assume only a single disk is attached to any SATA port, for reliability reasons)

Code:

               RAID 0
                   md2
                    |
     /---------------
     |              |            
   RAID 1         RAID 1        
    md0             md1           
  /------\       /------\       
  |      |       |      |       
500GB  500GB   500GB  500GB   
 sdc    sdd     sde    sdf

Now my doubt:

Ok, imagine a scenario such that after some time I implemented the above, I would like to add another RAID 1 with the aim of making more room available at the top level md2.
At this stage I would like to reach the following situation, without losing or having to backup somewhere else the data
already stored by the RAID array

Code:

           RAID 0
                   md2
                    |
     /-----------------------------\
     |              |              |
   RAID 1         RAID 1         RAID 1
    md0             md1            md3
  /------\       /------\       /------\
  |      |       |      |       |      |
500GB  500GB   500GB  500GB   500GB  500GB 
 sdc    sdd    sde    sdf      sdg    sdh

A similar question has already been answered, however I'd like not to split (if possible) my RAID as suggested here:

http://www.linuxquestions.org/questi...highlight=RAID

Instead, can anyone of you guys confirm the following is possible?

1. create RAID 1 of the two newly installed sata disks and call it md3

Code:

	mknod /dev/md3 b 9 1
	mdadm --create /dev/md3 --level=1 --raid-devices=2 /dev/sd[gh]
	mke2fs -j /dev/md3

2. add md3 to md2.... Data already stored on md2 should remain safe at all times and available storage space reported by md2 should expand by a further 500GB seamlessly....... am I correct????

Code:

 	mdadm --add /dev/md2 /dev/md3

Any comments are really welcome!

Cheers

ChrisAbela · 06-03-2008, 06:49 AM

I am not sure why you are asking these questions. Did you try it out before posting this question?

nibbiodagliocchiali · 06-03-2008, 05:25 PM

Quote:

Originally Posted by ChrisAbela

I am not sure why you are asking these questions. Did you try it out before posting this question?

yes, you are right, I should have explained why I am asking these questions.

Basically I would like to build a home storage server, but I'd like to check that the above proposed solution is feasible/likely to work before start buying motherboard, memory, hard drives, power supply and chassis

In other words I'm seeking opinion of experienced linux users before buying all the hardware (and spending around 1000 Euros), only to discover that maybe my understanding was wrong and no, sorry you can't do that...

Cheers

ChrisAbela · 06-04-2008, 01:31 AM

You do not need your server to try it out. You only need any Linux Box. I hope that I am not insulting your intelligence if I were to tell you that you may create a RAID on partitions of the same disk (for experimental purposes only). Even a Live CD will do, the only hardware you need is any Computer, a Live CD and a disposable Partition.