[DRBD-user] Re quest comments: DRBD to cold BackUp DMS with minimal DownTime

Bart Coninckx bart.coninckx at telenet.be
Fri Nov 12 11:51:52 CET 2010

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

On Thursday 11 November 2010 13:07:09 I. Schumacher wrote:
> Greetings.
> I am administrator of an Alfresco DMS running on an dedicated ubuntu server
> and is backedup to a streamer via a simple cron job.
> Unfortunately my predecessor (who set up this backup process) did not know
> that streaming a backup while the DMS is running causes mysql database
> inconsistencies preventing the DMS to boot after recovery. boo-hoo
> Running a proper cold back requires approx 2h while the DMS is shutdown.
> Thats just to long.
> One way would be to set up a slave-read-only-dms-site with mysql
> replication which can be shutdown for backup anytime while the master
> system is still running. In my opinion this is a waste of ressources
> because the slave site got to be up all the time, only building indices
> out of the replicated mysql data.
> In the course of an Upgrade to a newer version of the DMS I plan to
> implement a new backup process using DRBD involving a well equipped
> Master-DMS-Site and a MiniDRBD-Site for backup on another machine.
> 1. I have two virtual machines on two separate physical machines. VM1=
> MasterSite VM2=MiniDRBD
> 2. VM1 is running Ubuntu Server, RDBD, iptables, sshd, mysqld,
> oOffice-headless and tomcat.
> 3. Residents of VM2 are Ubuntu Server, RDBD, sshd and iptables
> 4. VM1 and VM2 use a virtual HardDisk /dev/sdb  each residing on the
> corresponding physical machine
> 5. RDBD repilicates "VM1/dev/sdb0" to "VM2/dev/sdb0" via /dev/drdb0
> 6. VM1 stores all DMS relevant data including mysql database and indices on
> /dev/drdb0
> To stream a cold BackUp with minimal DownTime I intend to use the following
> procedure:
> 1. crontab a shell script on VM1 which
> => stops DMS closing the database properly
> => RDBD replicates the closed state of the database to VM2/dev/sdb0 via
> /dev/drbd0
> => stops replication via "drbdadm disconnect MyFS"
> => starts the DMS again
> => waits for 2.5h and starts replication via "drbdadm connect MyFS"
> => exits
> 2. Five Minutes after 1. started I crontab a shell script on VM2 which
> => mounts VM2/dev/drdb0 to e.g. /media/drdb0
> => streams all files to tape via "tar cvf - /media/drdb0/* | dd
> of=/dev/str0/n block-size=4096"
> => umounts /media/drdb0
> => exits
> (I think that:)
> Streaming a BackUp that way reduces the downtime of the Master
> (VM1/alfresco) to about 10 seconds instead of 2 hours. Additionally it (i
> hope) nearly halves required CPU time and RAM usage in comparison to the
> mysql-replication approach that is recommended by the Alfresco-DMS vendor.
> (:but I may be wrong)
> Some general questions:
> Q1. I wonder if DRDB will autosync all changes made on the master during
> the "disconnect" to the slave after a "drbdadm connect MyFS" (in script 1.
> on VM1).
> Q2. How long will it take drbd to replicate the closed state of a 150mb
> database to VM2 so I can stop replication? (1GB/s LAN)
> Q3. What do you think would be the minimum specs for my miniRDBD machine
> (VM2). (128RAM,1core,256swap?)
> Q4. Do you have any suggestions how to use drbd a smarter way for my backup
> purposes.
> Q5. <Non drbd question> What is the best way to invoke all commands from
> only one script on VM1? Commands on VM2 will have to be executed as root.
> How can I do that without storing my root password as plaintext inside the
> script. I know I did that some time ago but I forgot how...
> I hope you can help me.
> Thanks a lot in advance. ;)
> Dramatic

Would using LVM snapshotting be a possibility? If you use it for your MYSQL 
storage, it can provide you with a stable readonly copy when you take it after 
shutting down MYSQL. If you use it for your VM storage, you could copy your 
entire guest after pauzing or saving it.


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