Adam Thornton wrote:
On Mon, 2004-05-10 at 09:16, Phil Hodgson wrote:
Does anyone run any hot standby systems on Linux 390? Is the data (if any) migrated and health checked by your own code or is there some software that I need to be made aware of?
There are certainly sites using the Linux-HA clustering code on 390. Although that's usually active-active rather than hot-standby.
Both systems are up and running the same apps at the same time. When one fails, the routers redirect incoming traffic to the second system, and it can then access the DASD of the failed first system. Works neat.....
You can also certainly define a second set of machines on a second frame with access to the same DASD, as a full-frame (or, with appropriate use of VIPA, a per-image) failover configuration. To do this really really right and with neat automation, you could use CSE, but even without it it's doable as long as your staff is trained to know that you never ever ever run the same image on both frames simultaneously. This gives you nearly-hot standby: when one image fails, a monitor of some kind (doesn't have to be sophisticated) kicks off its opposite number on the other frame. Failure detection takes some amount of time, and then IPL of the new guest takes a little longer.
The CSE that Adam mentions is the Cross Systems Environment (CSE) for z/VM. With it, two or more VM systems can share 1) the CP directory, 2) spool space, and 3) minidisks in a controlled and safe manner. Of course, this approach to Linux high availability systems only works with Linux running as guests of the VM systems.
Feel free to contact me off-list if you'd like all the gory details about setting up and using CSE in a HA Linux environment. The nice thing about CSE is that, if you have z/VM now, you already have CSE as well. It's just a matter of configuring and starting it up......
You could combine an approach like this with FlashCopy or PPRC or both, if you had the disk space to spare. Then you could recover the original image in parallel while its spare was running.
Adam
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