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mdadm level=raid10 - Anybody use it?

All of the how-to's list creating 2 levels of RAID - but I see a command in mdadm for --level=raid10
Should I use this - if so - how? What should the command look like?

I'd like to build a RAID 10 out of 7 SATA drives on centOS 5.2.

mdadm -v --create /dev/md0 --level=raid10 --chunk=8 --raid-devices=7 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1 /dev/sdh1

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cjl7

Well you can't.

Raid 10 (or 1+0) is two or more raid 1 (mirrored) that are Raid 0 (striped). So it dictates you to have at least 4 discs and then adding it with pairs.

Have a look at this page http://strugglers.net/wiki/Linux_RAID_best_practices to get information about the different raid levels.

http://tldp.org/HOWTO/Software-RAID-HOWTO.html is the "good old" howto.

//jonas

cjl7

The problem in your command is also that you are using --level=raid10 it should be --level=10

Modify the command and use 6 disks for the array and 1 as hot-spare.

mdadm -v --create /dev/md0 --level=10 --chunk=8 --raid-devices=6 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1 /dev/sdh1 --spare-devices=1

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smfx99

ASKER

The command I listed seems to be accepted and building fine.

It also supports an odd number of devices - as per the "Linux MD supports an odd number of devices for RAID-10."

Yes, we understand what a RAID is and specifically a RAID 10 consists of - but what about the command listed in the mdadm tool "--level=raid10" doing?

This is a single level RAID - as per - http://en.wikipedia.org/wiki/Non-standard_RAID_levels

cjl7

Yes, you are absolutely right! My bad!

If it is working and your array is coming up, what's the problem?

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mzalfres

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