Re: How to grow RAID1 mirror on top of LVM?

Hi Neil,

Thanks for your reply!

On 25 Mar 2008, at 05:36, Neil Brown wrote:

On Thursday March 13, aia21@cam.ac.uk wrote:

quoted

Is there a better way to do this?  I am hoping someone will tell me  
to
use option blah to utility foo that will do this for me without  
having
to break the mirror twice and resync each time.  (-;

Sorry, but no.  This mode of operation was never envisaged for md.
I would always put the md/raid1 devices below the LVM.

We do that already.  (-:  And then we put MD on top again.  What we  
have is two computers, each with six 500GB disks, set up as MD RAID-10  
+ 1 hot spare on the six disks.  Then run LVM on the MD RAID-10 and  
create two virtual drives on the LVM on each box.  Then on each box we  
have one of the LVM drives feed into an MD RAID-1 mirror and the other  
LVM drive is exported via iSCSI (iscsitarget) to the other box.  The  
iSCSI drive is then imported by the other box using open-iscsi and the  
resulting device is fed into the other half of the MD RAID-1 mirror on  
that box.

So yes, I am sure you never envisaged this mode of operation!  But it  
is a way to give us synchronous data replication across two sites  
(there are about 3 miles between the two boxes) with free software  
which in combination with my custom scripting and heartbeat2 allows us  
to fail the storage (the MD RAID-1 are xfs formatted and the NFS  
exported) over from one site to the other at the flip of a switch and  
in case of one machine blowing up, etc.

Every time you buy two drives, combine them into a RAID1, and add the
/dev/mdX as a PV for LVM.  Then grow you LVM devices whenever you
like.

quoted

If not, please consider this a feature request for mdadm.  (-:  It
should have an option to detect that the underlying device has grown
and thus write a new superblock  (or move the old one or whatever) at
the end of the newly grown device instead of complaining that it does
not exist.  Or something!  As it is, it is incredibly time consuming
and inefficient.  )-:

I'll keep it in mind (Which it to say:  I will save this in my 'mdadm'
mailbox, and have a look through that mailbox next time I'm working on
improvements to mdadm).

Great, thanks!

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/