On Fri, Jul 5, 2013 at 10:56 AM, Gene <gh5046@xxxxxxxxx> wrote: > On Thu, Jul 4, 2013 at 10:25 PM, denis bahati <djbahati@xxxxxxxxxxx> wrote: >> Hi Team, >> >> Thanks for the good explanation. >> >> If that is not workable for the database, can anyone recommend me for the >> setup of the database clients and data files in order to achieve HA and load >> balancing? How should I set up my VMs and stations (Two machines with two >> VMs each)? I will appreciate for a workable approach and that is practical >> for the HA/Load balancing. > > It depends on what database product you're using. If it's Oracle > Database Server it's designed to work with shared devices/file > systems. You shouldn't have a problem running it in an active/active > (load balanced) configuration. If it's MySQL/MariaDB the best you can > hope for, as far as I know, is an active/passive configuration with > replication. Oracle is hideously expensive in this mode. It basically uses a customized operating system, and it's *still* prone to the basic problem of locking transactions to avoid conflicts. They just expend a *lot* of system and software resources to manage it, which is why such a clustered Oracle database takes so much resources. There is "Multiple-Master MySQL", which basically provides built-in election of the master node and interesting load factors to split the load, and uses a separate IP address for the "master" node. It works pretty well and is available in the "mysql-mmm" package from EPEL. > I'm guessing you're using MySQL. Make your database highly available > in an active/passive configuration with replication and use some sort > of failover (heartbeat, carp, etc) or a network load balancer. > Depending on your application you can still run it in a active/active > (load balanced) configuration. Been there, done that, had *way* too many places just wave their hands at the failover and never actually configure it. mysql-mmm takes a lot of the guesswork out. >> >> Regards >> >> ________________________________ >> From: Nico Kadel-Garcia <nkadel@xxxxxxxxx> >> >> To: denis bahati <djbahati@xxxxxxxxxxx>; Discussion about the virtualization >> on CentOS <centos-virt@xxxxxxxxxx> >> Cc: "brett@xxxxxxxxxxx" <brett@xxxxxxxxxxx> >> Sent: Thursday, 4 July 2013, 18:32 >> >> Subject: Re: KVM virtual machine and SAN storage with FC >> >> On Thu, Jul 4, 2013 at 12:44 AM, denis bahati <djbahati@xxxxxxxxxxx> wrote: >>> Hi Brett, >>> >>> On my plan is as follows: >>> >>> I have two machine (Server) that will host two VM each. One for database >>> and >>> one for application. Then the two machine will provide (Load Balance and >>> High availability). My intention is that all application files and data >>> file >>> for the database should reside on the SAN storage for easy access and >>> update. >> >> Don't... do this. Two database clients writing to the same database >> filesystem back ends, simultaneously, is an enormous source of excited >> sounding flow charts and proposals which simply do not work and are >> very, very likely to corrupt your database beyond recover. These >> problems have been examined, for *decades* with shared home >> directories and saved email and for high performance or clustered >> databases that need to not have "split brain" skew, It Does Not Work. >> >> Set up a proper database *cluster* with distinct back ends. >> >>> Therefore the storage should be accessible to both VMs through mounting >>> the >>> SAN storage to the VMs. The connection between SAN storage and the servers >>> is through Fiber Channel. >> >> Survey says *bzzzt*. See above for databases. For shared storage, you >> should really be using some sort of network based access to a >> filesystem back end. NetApp and EMC spend *billions* in research >> building high availability shared storage, and even they don't pull >> stunts like this the last I looked. I can vaguely imagine one of the >> hosts doing write access and the other having read-only access. But >> really, most databases today support good clustering configurations >> that avoid precisely these issues. >> >>> I have seen somewhere talking about DM-Multipath but i dont know if this >>> can >>> help or the use of VT-d if can help. I will also appreciate if you provide >>> some links to give me insight of how to do this. >> >> Multipath does not mean "multiple clients of the same hardware >> storage". That's effectively like letting two kernels write to the >> same actual disk at the same time, and it's quite dangerous. >> >> Now, if you want each client to access their own fiber channel disk >> resource, that should be workable. Even if you have to mount the fiber >> channel resources on the KVM host, and make disk images for the KVM >> guest, that should at least get you a testable resource. But the >> normal approach is have a fiber channel storage server that makes disk >> images available via NFS, so that the guest VM's can be migrated from >> one server to another with the shared storage more safely. >> >> >> >> _______________________________________________ >> CentOS-virt mailing list >> CentOS-virt@xxxxxxxxxx >> http://lists.centos.org/mailman/listinfo/centos-virt >> > _______________________________________________ > CentOS-virt mailing list > CentOS-virt@xxxxxxxxxx > http://lists.centos.org/mailman/listinfo/centos-virt _______________________________________________ CentOS-virt mailing list CentOS-virt@xxxxxxxxxx http://lists.centos.org/mailman/listinfo/centos-virt
