Hi folks, An interesting debate over the best HA setup up with MySQL on System z is now motivated me to reach out to the community to ask for your opinion.
We have 2 production LPARS on a z/10 running Red Hat v5.3 and are connected in a common lan segment using vswitch. On each LPAR the customer wishes to have an MySQL database server: one master (as primary) and one slave (as a failover for backup). If the primary fails, the database gets umounted and mounted RW on the slave host.. ip takover happens and mysql starts up on the filesystem that was swapped over. The question simply is - what is the best high availability setup to allow for this scenario to happen? A few options that have lead to good debate: 1) Because the database will be 200-300GB, we can use LVM and have it available to mount RW on either system. We need to be very careful not to mount RW at the same time; else we risk destroying the data. In cases where customers are using VMWARE or Xen on distributed, you ensure this by using PaceMaker to tell the hypervisor to issue a STONITH to totally kill the primary machine. This ensures, that the filesystem will be RW only on the backup now. However! There is currently no capability on z/VM to allow PaceMaker (or any other software that I know of) to do this. Instead, we may be able to configure PaceMaker to issue a #CP LOG off command, but how do we get this message across to the 2nd LPAR? Perhaps CSE (Cross - System - Extensions) will allow for it? Or perhaps it would be easier to host these two servers on the same LPAR. Thoughts? 2) To avoid the playing around with the issues in (1), we then thought to use the data replication in MySQL instead; replication happens with the primary writing what insert / delete statements the slave needs to run into a bin.log file - which is single thread and serial. The slave runs this in sequence in the efforts to try and match what the master is getting. However, our MySQL experts tell us that because of the single thread nature of this asyncronous replication, there is risk that the slave server won't be able to catch up. Since the database will be running with 800 transactions / second, in the event of a failover, many tranactions will be lost. Thus, MySQL support recommends to use DRDB filesystem block replication instead. I wonder - any takers for this option? Concerns for performance? Any thoughts will be appreciated it. I also saw somebody write about putting a NFS up and then use it over hipersockets. This seems simple, but alas, 800 transactions per second on a NFS system - performance issues looming? Any thoughts are welcomed. Thanks! - Frank Pani ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
