<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
Hi,<br>
<br>
Lionel Sausin wrote:
<blockquote cite="mid:4D2C39EE.9040105@numerigraphe.com" type="cite">Dear
DRBD community,
<br>
We are setting up a 2+1 node cluster :
<br>
- A is master
<br>
- B is slave
<br>
- S is an additional spare/backup machine, disconnected most of the
time
<br>
The use cases are :
<br>
- Normally we sync S once a week then unplug it and keep it safe. The
dataset is big (26To) so it has to catch up fast.
<br>
- Of course when A fails we promote B
<br>
- But when either A or B fails, we still want HA: so we plug S in and
keep it synced until the failed machine is repaired
<br>
<br>
So we intend to set up DRBD between A and B, and use a stacked DRBD
resource to replicate (A+B) to S.
<br>
<br>
My question is: if A or B dies and can't be fixed, can S be
reconfigured to replace it without a full sync?
<br>
</blockquote>
You usually leave S disconnected, that's why you need a full sync to
bring S up to speed, but normally what you would do when using stacked
resources would be to configure S with protocol A, this is actually the
recommendation in the drbd.org docs
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<a
href="http://www.drbd.org/users-guide/s-three-nodes.html#s-three-node-config">http://www.drbd.org/users-guide/s-three-nodes.html#s-three-node-config</a><br>
<br>
This way S will have the most recent information with as little
performance overhead as possible due to protocol A. <br>
<blockquote cite="mid:4D2C39EE.9040105@numerigraphe.com" type="cite">In
other words: can a setup like (A->B)->S be changed to (A->S)
with a quick sync?
<br>
</blockquote>
You need A->B, and you can only setup one replication link that
spans 2 servers (e.g.: you can't set A's /dev/drbdx to replicate to
both B and S at the same time), the only way to do it is to set normal
A->B, and on top of that AB->S, because you don't know if A or B
will be up and don't want to manually choose (if it was somehow
possible) to sync A->S or B->S depending on which (A or B) is up.
Stacked resources does that for you automagically, it syncs whomever is
Primary to the stacked resource (S).<br>
<br>
Read up on differences between protocol C and A, if you haven't
already, test it to see what is the performance penalty due to the
overhead (27To -> you must be French :P) of the large dataset will
be. Come back if you have more questions.<br>
<br>
Regards,<br>
Dan<br>
<blockquote cite="mid:4D2C39EE.9040105@numerigraphe.com" type="cite"><br>
Thanks in advance if you can share your knowledge.
<br>
<br>
Lionel Sausin
<br>
_______________________________________________
<br>
drbd-user mailing list
<br>
<a class="moz-txt-link-abbreviated" href="mailto:drbd-user@lists.linbit.com">drbd-user@lists.linbit.com</a>
<br>
<a class="moz-txt-link-freetext" href="http://lists.linbit.com/mailman/listinfo/drbd-user">http://lists.linbit.com/mailman/listinfo/drbd-user</a>
<br>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Dan FRINCU
Systems Engineer
CCNA, RHCE
Streamwide Romania
</pre>
</body>
</html>