I hope I can articulate my question as precise as possible.
I am seeking for a way to make backups for my vm-servers as soon and frequent as possible as the data they are handling/producing are valuable. I have a KVM-Host and at least 2 Guests: Webserver (Apache/PHP) and Database server (MySQL/Solr). I don't care much about the host, but the guests. I don't want you to get deep into KVM or virtualization for this topic. This thread should be applicable to all vm based environments and all other environments as well. The vm scenario suites well because it is more tricky and represents one of the most complex situations in my imagination. At least, I need that on this basis.
Currently, I have in-vm backups and LVM-based snapshots which I generate 1-2 times a day. In case of a hardware failure (which I had recently) I miss a whole bunch of data in the best case.
So, one way could be to go down on each application/service and apply the best backup strategy available. Should be considered in each case.
Another interesting way seems to be the use of a distributed file system. The idea is to have a file system that acts slightly like the binary-log of MySQL. Or more general: It captures all write-actions on the file system and replicates it to another machine asynchronously. Depending on the network and the amount of data written, this can end up in seconds or minutes of latency and needless to say it misses all actions that are held back in cache. So I have a vm that is sitting on a distributed file system which is installed on the vm-host. Every write-action gets then asynchronous applied on a (say) backup-server. When it now comes to an hardware failure I can switch to the backup server (in theory) as the new master or simply copy the files back to the restored master-server in case, downtime is more acceptable than data loss. The effect should be that the virtual machine acts like it was turned of immediately seconds to minutes before. But not hours. I do not seek a master-master replication on file-system level, as this is not supported by most applications, especially database servers like MySQL!
So my question is: Is there anyone who has already made some experience with such configurations or has knowledge which is positive as well as negative for this attempt to backup data? I have no deep experience with these file systems. Especially on reliability and performance.