[CentOS] CentOS 6.2 software raid 10 with LVM - Need help with degraded drive and only one MBR

Luke S. Crawford lsc at prgmr.com
Mon Mar 5 22:52:16 EST 2012


On Mon, Mar 05, 2012 at 06:12:52PM -0500, Ross Walker wrote:
> Technically if the data portion is a true RAID10 you would only need to mirror /boot to sdb, cause if both sda AND sdb are out then the whole RAID10 is SOL and there would be no need to boot off of sdc or sdd.

> Having said that though it's just easier to create a 4 disk raid1 of /boot and duplicate the MBR across all of them.

I'm using the linux 'raid10' md type.  It actually allows an odd number of 
disks;  it just guarantees that each chunk of data is on at least two drives;

So yeah, rather than trying to guess on which chunk is where, I think a 
mirrored /boot is the easy way out.  

I did used to create mirror sets and stripe across them using LVM stripeing.
(Before that I actually used LVM mirroring, but it seems that nobody uses 
LVM mirrororing)

Anyhow, my ancidotal experience is that the linux md 'raid10' option
results in an array that rebuilds like twice as fast as two mirrors
that you stripe across with LVM.  

But yeah, either way, md0 was a small mirror across all drives.   
(and remember to load the bootloader on all drives.  It's in my kickstart
so I can't forget on setup, but I still need to be careful when I replace
drives.)

> Sounds like the hosting provider isn't very Linux savvy. I would always double check the setup of any system someone else installs for you.

As a general rule, if you want your hosting provider to support more
than just the hardware, you have to setup the software their way.  I mean, 
I'm guessing that you asked this hosting provider 'Hey, can you setup 
software raid for me?' and they did, even though they don't usually.  
I mean, if they setup software raid usually and still haven't solved this, 
then they are just plain incompitent;  I'm just saying, if this is an 
unusual setup for them, it might be the 'I haven't done this before' kind 
of incompitence, which we all suffer from time to time.  


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