[DRBD-user] Best way to use LVM with drbd

Rudi Ahlers Rudi at SoftDux.com
Fri Feb 15 14:13:42 CET 2008

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



Lars Ellenberg wrote:
> On Thu, Feb 14, 2008 at 11:04:59PM +0100, Rudolph Bott wrote:
>   
>> Harald Rinker schrieb:
>>     
>>> Hi @all
>>>
>>> What is the best solution to use LVM with drbd
>>>
>>> i think there are 2 possible way?s to do so
>>>
>>> 1. drbd on top of lvm
>>>       
>> I wouldn't recommend this - there's almost no point in this kind of 
>> setup because you loose all the flexibility of LVM and its dynamic 
>> logical volumes!
>>
>>     
>>> 2. lvm on top of drbd
>>>       
>> this is quite the way to go, but MAKE SURE (via /etc/lvm/lvm.conf or 
>> whatsoever) that LVM *only* scans the drbd devices under /dev/
>> Otherweise it might find the underlaying device (/dev/sdX or /dev/mdX 
>> etc.) and brake your whole setup!
>>
>> If you need to extend your storage you can add another drbd device 
>> (maybe on top of another raid device or a new harddisk etc.) and add it 
>> to your LVM setup as a new physical volume. Then extend your volume 
>> group(s) to also use the new physical volume and you're done.
>>
>> On top of that don't start LVM on the server which is currently the 
>> secondary - it won't be able to find the LVM metadata on the drbd volume 
>> because it is locked by the system. Which means if you fail over you 
>> have to restart LVM/re-run the checks on the new primary to make sure 
>> the system 'sees' all  of the volumes that have been 
>> added/changed/removed on the old primary before it went down.
>>
>> Another point is that you can use snapshots of your logical volumes to 
>> create backups etc.
>> Having drbd ON TOP of lvm would mean that you could only create 
>> snapshots of logical volume(s) containing the drbd structures - which is 
>> quite pointless in my eyes...
>>     
>
>
> both have their purpose. you can even mix both, if you can deal with the
> additional administrative complexity.
>
> having drbd sitting on top of an lv is nice: you can replicate "just
> enough" data, then grow later as the file system fills up.
>
> snapshotting below drbd is a nice feature as well: you can snapshot the
> secondary, and mount the snapshot on the secondary, for
> backups/reports/consitency checks.
>
> having a few drbd on lvm gives you the flexibility to migrate resources
> independently.
>
> having lvm on drbd makes your snapshots fail over with the resource
> itself.
>
> neither way is "better" per se, it always depends on your needs.
>
>
>   

Ok, so just to understand this. Let's say I want to setup RAID + LVM + 
DRBD, with the option of growing the whole storage with minimal fuss, do 
you recommend the following?

4x 250GB HDD's setup as RAID 5 (1x spare), with LVM on top of that, and 
DRBD on top of the LVM? And then, I can just replace the 250GB HDD's 
one-by-one, and increase the LVM ?

Kind Regards
Rudi Ahlers
CEO, SoftDux
Office: 087 805-9573
Fax No: 086 609 6128
Cell:   082 554 7532


Web:   http://www.SoftDux.com
Forum: http://Forum.SoftDux.com

Join SA WebHostingTalk today, on http://www.WebHostingTalk.co.za





More information about the drbd-user mailing list