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<TITLE>RE: Food for thoughts please - DRBD GFS2 CLVM etc</TITLE>
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<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Hello again,</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">After one more good thought, it looks to me that my major unknown parameter is how to control the Split Brain situation via Cluster Manager.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">All those days I am googling but could not find anything apart from HA references.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">To resolve SB, I can only use heart beat?</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#0000FF" SIZE=2 FACE="Arial"> There is no way to use the dopd and the other scripts via</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT COLOR="#0000FF" SIZE=2 FACE="Arial">cman?</FONT></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Thank you again for your time.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">Theophanis Kontogiannis</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Tahoma">_____________________________________________<BR>
</FONT></SPAN><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B><FONT SIZE=2 FACE="Tahoma">From:</FONT></B></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Tahoma"> Theophanis Kontogiannis<BR>
</FONT></SPAN><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B><FONT SIZE=2 FACE="Tahoma">Sent:</FONT></B></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Tahoma"> Wednesday, March 12, 2008 5:17 PM<BR>
</FONT></SPAN><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B><FONT SIZE=2 FACE="Tahoma">To:</FONT></B></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Tahoma"> drbd-user@lists.linbit.com<BR>
</FONT></SPAN><SPAN LANG="en-us"><B></B></SPAN><SPAN LANG="en-us"><B><FONT SIZE=2 FACE="Tahoma">Subject:</FONT></B></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Tahoma"> Food for thoughts please - DRBD GFS2 CLVM etc</FONT></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Hello All,</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">I am sending this e-mail to the list to ask for food for thoughts.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">I have two same servers based on AMD x2 64bit loaded with CENTOS5. </FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Memory and resources are not a problem since I begun with small systems and can expand up to 8 SATA disks, 2 IDE, 16GB RAM.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Now I have the same setup for HDs on both of them. One 80Gbyte and one 320Gbyte both IDE and sharing the /boot and / in RAID-1. </FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Also the left over space on both of them will be used as DRBD devices (that is /dev/hda4</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="Wingdings" SIZE=2>à</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial"> /dev/drbd0 and /dev/hdb4</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT FACE="Wingdings" SIZE=2>à</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial"> /dev/drbd1) in primary/primary config.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">What I plan to have as active applications are:</FONT></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">1. </FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT SIZE=2 FACE="Arial">ORACLE</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">2. </FONT> <FONT SIZE=2 FACE="Arial">MySQL Production</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">3. </FONT> <FONT SIZE=2 FACE="Arial">MySQL Development</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">4. </FONT> <FONT SIZE=2 FACE="Arial">Apache</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">5. </FONT> <FONT SIZE=2 FACE="Arial">storage for documents </FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">6. </FONT> <FONT SIZE=2 FACE="Arial">and in the future compilation and execution of MPI based code</FONT></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">I have thought about the possible implementation and I end up with two scenarios.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">FIRST:</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">/dev/drbd0 and /dev/drbd1 are members of one physical volume. Then running cman, gfs2 and clvmd, I create on large logical volume out of them, and then I format it as GFS2. All the disk space is simultaneously available and mounted as GFS on both servers. I create the directories with proper permissions that the applications will use. Using system-config-cluster or COGNA, I configure the services I want, and “run” them on the nodes I select.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">It looks that this scenario gives me the good option of live backup on either node (since the whole FS is mounted at the same time to both nodes), simple application migration if a node fails and easy expansion of the file system (I add on the PV the new /dev/drbd when I add a new disk and then expand gfs2). That way I keep a coherent image of my files and at the same time I can keep on adding disks, applications or whatever easily. </FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Now it seems to me that the problem with this setup, is how to make exploitation of the cluster manager (RHEL 5), in a way that will auto migrate the applications if the DRBD fails on one node. Is there any way to exploit the CMAN instead of heartbeat to manage first of all the underneath DRBD devices? And then how will cman be aware that it must not start the application because the FS could not be mounted? Maybe use a custom script as resource?</FONT></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">SECOND: </FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Again /dev/drbdX are members of the same physical volume. </FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">However this time, I create separate LVs formatted with ext3, one for every application that will run. Then with CMAN I create as resource also the LV to be mounted prior to the start of the service that is using it. In this it looks like the question of the previous scenario, on how I will control via CMAN the DRBD devices is some how solved. If it can not mount the LV this means that there is a problem with DRBD. But in that case the service is related to prior mounting the respective LV so it will not start.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">However I think that this does not scale well and also it looks like I will have an issue with backup.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">For backup I will use an external USB disk connect to one of the server, via which the already mounted FSs will be backed up!</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">I appreciate your comments and sharing your experiences.</FONT></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Sincerely,</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT SIZE=2 FACE="Arial">Theophanis Kontogiannis</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
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