[DRBD-user] Resources for learning how to use DRBD as Primary/Primary?

[D. Dante Lorenso]

Lars Ellenberg wrote:
> On Tue, Nov 20, 2007 at 11:34:17AM -0600, D. Dante Lorenso wrote:
>> All,
>>
>> I'm interested in being able to share a file repository from 2 
>> geographically remote locations and was interested in setting up DRBD to 
>>  replicate between the 2 nodes.
>>
>> I'm using CentOS 5 for my platform.  Does anyone have any documentation 
>> or howtos on what I need to do to set something like this up?
> 
> what is your understanding of "Pirmary/Primary"?

If I have 2 nodes, I'd like to use either node and have changes 
reflected on both.

>   do you want to use a cluster file system on top of that?
>   or do you want to have each site active for *its set* of shares,
>   and be the backup only for the respective other site's set?

I'm exploring OCFS2, GFS, and Lustre in addition to my DRBD testing.

> what does "geographically remote" mean in link latency and bandwidth?
 >  30 km FO dedicated 1Gbps low latency feeling for all practical 
purposes almost like a lan?
 >  3000 km 1Mbps flaky high latency bell wire?

Regular internet bursting to 100 Mbps at each location, but likely to be 
throttled to just 1-10 Mbps for this purpose.

> what is "a file repository"? what kind of files?

Mostly media files audio/video/telecom.

>  why would you need synchronous replication, why would rsync not do?

Currently rsync does the job.  With synchronous replication, though, I'd 
be able to write a file locally then trigger a remote job to begin using 
that file immediately.  Rsync works but is slow and we are syncing such 
a large number of files that the sync consumes a great deal of resources 
on both the sending and receiving sides.  I've also been meaning to look 
into csync2.

> what is your expected storage size?
 > what is your estimated average write rate?
 > what is you estimated peek write rate?

I'm at 6 TB now.  We have been doubling storage each 6-12 months.  The 4 
TB limit on DRBD makes me look at DRBD+, but the licensing costs there 
have us concerned.

I see that the drbd.org site says: "Since DRBD-8.0.0 you can run both 
nodes in the primary role, enabling to mount a cluster file system (a 
physical parallel file system) one both nodes concurrently. Examples for 
such file systems are OCFS2 and GFS."

I was hoping there was a nice tutorial/howto on specifically this type 
of Primary/Primary configuration.

-- Dante