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Hello,<br>
<br>
Thanks for replying Lars.<br>
<br>
I just wanna light up points that were not clear... (looks below please)<br>
<br>
Lars Ellenberg a écrit :
<blockquote cite="mid:20090212204349.GA10065@barkeeper1-xen.linbit"
type="cite">
<pre wrap="">On Thu, Feb 12, 2009 at 05:02:32PM +0100, Julien Reveillet wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Hello,
I have a very special configuration to set up.
I need to have 2 servers running CentOs 5 with a mysql server 4.0.21 (
that a must do...).
The data base directory needs to be replicated between both servers with
one mysql server running with read-write access and the other with
read-only access.
The production server (mysqld with rw access) which is highly loaded
needs to not be impacted by drbd accesses ( it can be a little bit ) and
the web server (mysqld with ro access) can be asynchronous for some
minutes with no problems.
For now, i choosed to use drbd 8.2.6 with ocfs2.
It is set up and running correctly on the same lan with a descent sync
rate but i will have to try it soon over a wan network.
On what i've tested and read, i can't use protocol A for this scenario
as the option "allow-two-primaries" needs only protocol C.
The whole database directory is about 70GB which is quite huge to full
sync over a 2M wan network. For sure, i will do the first sync over a
lan but i'm afraid of cases where drbd will go to standalone and will
need a full resync.
So my questions are :
- Falling to standalone mode will automaticly needs a full resync?
</pre>
</blockquote>
<pre wrap=""><!---->
No. Why?
</pre>
</blockquote>
While testing, i did not found the correct way to reattach ressources
without a full resync (anyway, it's because i'm a newbee, don't bother
with this)<br>
<blockquote cite="mid:20090212204349.GA10065@barkeeper1-xen.linbit"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">- Can this kind of scenario be possible to work on or not ?
(if not, do you think of another solution?)
</pre>
</blockquote>
<pre wrap=""><!---->
If you _want_ asynchronous replication,
why would you go for a synchronous replication solution?
why not go for mysql replication, if that is actually what you want?
cluster file lock manager latency and all sorts of issues
with a WAN link will be a real pita.
</pre>
</blockquote>
I want the replication as synchronous as possible but as we're doing
with a wan network...<br>
I know about the mysql replication which is true and is what we need
but, we need to pay a very expensive licence to the developper for this
so i wanted to find another cheaper solution. As i have no more
choices, i will probably do with it.<br>
<blockquote cite="mid:20090212204349.GA10065@barkeeper1-xen.linbit"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">- Will protocol C cause many heavy lags on my production server ?
(i guess yes but...)
</pre>
</blockquote>
<pre wrap=""><!---->
the replication link is 2 megabit/second,
which is roughly 200 kByte per second.
and the latency is what? 200 msec?
well, DRBD cannot magically improve those numbers.
I don't think that would be feasibly for a cluster file system.
and not at all for a data base on top of a cluster file system.
</pre>
</blockquote>
I do not expect Drbd to be Harry Houdini... ;-) but i thought it can
work if protocol A was useable with both primary nodes.<br>
Anyway, drbd is a very good software and i would love to have another
scenario to do with it.<br>
<br>
Thanks for the good work.<br>
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