When using these legacy SAN DR solutions the worst of part of it comes when a site fails and the applications have to be manually started up on the remote site. This requires setting up all the fun stuff that exists on the primary site including storage replication transaction log analysis, remapping HBAs to LUNs and security setup; LUN masking and switch zoning. If the link went down instead of a site, transactions could have been written to the remote site without the acknowledgment being received by the primary site. This can result in what’s referred to as a “split brain”, which means that you may have to completely rebuild the primary site from the secondary site, or play around with logs for hours to determine which transactions went where.
The good news is that times have changed. First of all, with iSCSI, it’s all IP end-to-end and you only have one network to manage. And TCP/IP takes care of transmitting over any latency, so you don’t have to worry about any specialized gear to get your data to the other side.
The LeftHand SAN technology not only offers an iSCSI-based solution, but is the only SAN solution in the industry that can create virtual, redundant volumes that span multiple sites. What this means is that servers see the same volumes, and connect to the volumes through the same IP address (or a different IP address or subnet, your choice) at each site. This makes life very simple when failing over servers and virtual machines. For example, when combined with VMware HA, a site failure can be detected within 15 seconds and the virtual machines started up within a minute at the remote site—as opposed to the several hours that are typically required for an administrator to physically go to the site and bring the servers online and connect the VMs to a different SAN with distinct volume copies. When failing over to a secondary location with the LeftHand SAN, the virtual machines are connecting to the exact same SAN volumes that they were connected to at the primary site. In other words, your data is always online, and it’s just a matter of getting your servers and virtual machines re-connected to the always-available SAN volumes. This can be setup for redundancy across racks, floors, buildings and sites many miles away.
What’s really cool is to think about what lies ahead. Take VMware’s Fault Tolerance software, for example. VMware Fault Tolerance is leading-edge technology that provides continuous availability for applications in the event of server failures. It does this by creating a live shadow instance of a virtual machine that is in virtual lockstep with the primary instance. By allowing instantaneous failover between the two instances in the event of hardware failure, VMware Fault Tolerance eliminates even the smallest of data loss or disruption. When you combine this with LeftHand’s Multi-site SAN capability, you end up with true HA and DR with no reboot and seamless cutover; you can power off a site with no interruption to end users.
There is also LeftHand Remote Copy software that has very similar capabilities, but works over slower, higher latency links, and is certified with VMware SRM. What’s really remarkable is that LeftHand’s Multi-site SAN and Remote Copy software are both included with all of LeftHand’s SAN products, and managed from the same GUI. We figure customers should have this capability whether they plan to use it now or not, because we believe some day they will want to setup an HA/DR environment, or remote backup site, and the software will be ready. And in most cases they won’t need to purchase a new LeftHand SAN for the remote site, just spread the existing SAN across both sites. Remote offices can also be replicated automatically back to a central site with the use of LeftHand’s Virtual SAN Appliance, with no additional SAN hardware purchases required.
Now that’s HA and DR the way it should be. Stay tuned, we have some great DR events coming to a city near you.