vSphere Availability

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  • 1.  HA, how to synchronize two servers with one data storage each

    Posted Aug 03, 2012 04:33 PM

    Hello,

    i do not have any experience with ESX5.0i and vSphere5.0, but I need some help for planning a hardware infrastructure. So, I try to approach the problem from the hardware side (with the background I have), but I dont know much about ESX5.0i / vSphere5.0 capabilities and if it can do what I want it to do.

    I know there there are High Availability setups, with two synchronous servers (nodes), which are connected to one data storage. Typicalliy, in such a HA setup, each server has two SAS controllers, which communicate to an external data storage which has a dual controller SAS. It´s the typical dual domain / dual path setup. In case one server (or one controller or one cable) fails, the other server continues all tasks. It´s a master/slave concept that is used here in the disk driver which determines which server is allowed to write on the RAID, and which server is not allowed. Personally, I do not really like this concept with two servers and one data storage, because if the one data storage fails, it´s basically game over. So a setup with two servers and two data storages looks better to me.

    In addition to that, as the setup with the dual path is kinda complex, and the special pricy hardware for it is only provided by very few companies like IBM or HP, I like to know if it is possible to build two identical servers from standard parts, and achieve nearly the same level of HA (the above mentioned concept of 2 servers and 2 data storages).

    Let´s assume we have two servers, with enough memory, and each has 10 disks in a Raid for that.

    Questions:

    1.) Is it possible to use ESX5.0i / vSphere 5.0 in a HA setup, so if one server fails, the other one continues the tasks? From the standard HA setup described above (2 servers, 1 storage), I know it´s generally possible, but my question is if it also works with 2 servers and 2 storages (each server has its own storage).

    2.) If one server fails, for example by hardware malfuction, and the server is repaired and restarted the next day, how does this system synchronize again with the other functional system? The data on the storage is not synced anymored, so i assume this needs to be done first on the fly, and secondly then the server needs to be put in a state that it can start doing the same things as the first server again to provide fault tolerance. The question I have is: how does it synchronize the data storages on the two computers? A standard backup solution wouldnt help much as the source data also changes during the backup process, so I assume the only way would be if ESX / vSphere has some functions for that.

    A few keywords, a brief explanation, or a link would be of great help for me to understand how the this can be solved.



  • 2.  RE: HA, how to synchronize two servers with one data storage each

    Posted Aug 03, 2012 09:13 PM

    Hey  TGquattro

    1) Basically yes, you cluster multiple ESXi 5 host inside a Cluster (requires a vCenter Server) and a shared storage for all of the hosts.

    The shared storage must be a "stand alone" system which provides a LUN via iSCSI or FC with will be VMFS formatted or it also could be an NFS share.

    Your VMs will reside/saved on this shared storage and they will run on one of the hosts inside the cluster. In case one server crashes the remaining hosts are able to restart! (= short downtime) the VM which have been running on the failed hosts. This is possible because the remaining hosts are able to access the virtual disks of the VMs on the shard storage.

    In case you need a fail over without downtime you need the "fault tolerance" feature, but then you'll some restrictions regarding your virtual machines hardware.

    Normally you can't use a local storage on each host to build a shared storage / HA cluster. BUT maybe the new "VMware Storage Applice" is something you should think about. The appliance enables you to put your local storage together and serves this storage as shared! NFS Datastore to all hosts.

    http://www.vmware.com/products/datacenter-virtualization/vsphere/vsphere-storage-appliance/overview.html

    2) It's unlikely that your ESXi installation will be corrupted or damaged but in case there are several methods to bring it back online like:

    - Manuall reinstall (maybe already with a kick start script to provide the basic config)

    - Manuall reinstall and manual config

    - Manuall reinstall and applying a host profile wich you created earlier from a reference host. The profile contains your standard settings for your hosts.

    - Auto deploy (which provides a PXE boot environment for your ESXi hosts, so every boot will be a kind of new (stateless) installation, your ESXi will run just in RAM. (Slightly oversized for the start)

    And storage doesn’t need to get synced, because you are using a central shared storage.

    But I recommend you to maybe buy a book to dive into all this techniques and features.

    If you have any further questions let me/us know.

    Regards

    Patrick



  • 3.  RE: HA, how to synchronize two servers with one data storage each

    Posted Aug 03, 2012 09:44 PM

    Welcome to the Community - VMware HA configuration has both host running independently hosting their own VMs running on shared storage - VMware HA monitors the two hosts and records the VMs that are runing - if a host it is recognized bythe HA cluster and the VMs thatw ere running on that host are restarted on the remining nodes.

    1.) Is it possible to use ESX5.0i / vSphere 5.0 in a HA setup, so if one server fails, the other one continues the tasks? From the standard HA setup described above (2 servers, 1 storage), I know it´s generally possible, but my question is if it also works with 2 servers and 2 storages (each server has its own storage).

    Not with two storage devices with software available from VMware - VMware HA requires shared storage - SAN - FC oe iSCSI and NAS/NFS

    2.) If one server fails, for example by hardware malfuction, and the server is repaired and restarted the next day, how does this system synchronize again with the other functional system? The data on the storage is not synced anymored, so i assume this needs to be done first on the fly, and secondly then the server needs to be put in a state that it can start doing the same things as the first server again to provide fault tolerance. The question I have is: how does it synchronize the data storages on the two computers? A standard backup solution wouldnt help much as the source data also changes during the backup process, so I assume the only way would be if ESX / vSphere has some functions for that.

    From above it doesn't - VMware HA relies on shared storage -

    To learn more check out the section on VMware HA in http://pubs.vmware.com/vsphere-50/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-501-availability-guide.pdf



  • 4.  RE: HA, how to synchronize two servers with one data storage each

    Posted Aug 03, 2012 11:03 PM

    With VSA, you would be able to leverage your drives and use them as 1 shared storage

    http://www.vmware.com/products/datacenter-virtualization/vsphere/vsphere-storage-appliance/overview.html



  • 5.  RE: HA, how to synchronize two servers with one data storage each

    Posted Aug 10, 2012 02:00 PM

    A storage Virtual Appliance definately sounds like a good fit, as you can achieve the same result at a fraction of the cost.

    So essentially a storage appliance wouild sit on each host an utilize the internal disk capacity, mirror up between 2 + servers and present that as shared storage to enable VMware HA.

    StorMagic SvSAN is one solution that is very flexible and allows the end-user to present that data to the SVAs as they see fit and to utilize non-identical server hardware.

    Heres an FAW comparion we did some time ago which I think lays out some of the functionality quite nicely. http://www.stormagic.com/svsan_vmware_vsa_comparison.php

    Thanks

    Steve