[DRBD-user] software RAID, LVM

Nate Reed nreed at awarix.com
Thu Feb 2 17:41:45 CET 2006

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


Anyone have experience setting up DRBD on software RAID, possibly using LVM?  
I have never setup software RAID or LVM before, so I'm curious about how this 
is done.

Right now we have hardware RAID 1, so all data is redundant, and a /shared 
partition that is replicated across the network using DRBD.  

If we switch to Software RAID 1, would you have DRBD accessing a Linux RAID 
device or a logical volume?  Can you even put DRBD on top of a volume, since 
the underlying device has to be a block device?  

Here's what I was thinking of doing on each machine:

disk 1
  - swap partition
  - / partition
  - Linux RAID partition
  
disk 2
  - Linux RAID partition

Then, create a RAID device out of the two Linux RAID partitions, then put DRBD 
on top of this device  

The other setup I was considering is:

disk 1
  - Linux RAID partition

disk 2
  - Linux RAID partition

Then, create a RAID device out of these partitions, and create logical 
volumes /, swap, /shared, etc.  Then, have DRBD replicate one of these 
volumes.
 
Finally, there is a 3rd option, but I'm not sure this makes any sense: as 
above, put logical volumes /, swap, /shared, etc., on the RAID device, and 
use DRBD to replicate the entire device to the other node.  This doesn't make 
much sense since some data -- esp. swap -- should be local to each machine.  

So, what do you think? 

1. Have DRBD replicate a logical volume (/shared).  Is this possible?  Is 
there a block device associated with a lv?
2. Have DRBD replicate a /shared partition on RAID, and keep swap and / on 
disk #1.  Obvious downsides: no redundancy of swap and root, and wasted space 
on disk #2.

Am I missing some other approach?

Thanks,
Nate



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