The Latest In High Availability
This is essentially a short conceptual technology update, nothing
more. I'll approach it on a 'helicopter' level and we can drill down
in detail in coming newsletters.
High Avalailability is usually expressed in '9-s'. Three nines is
99.9% uptime, and over a year that is dozens of hours downtime.
Four nines is more like it. This is downtime measured in hours
instead of days. Five nines is the holy grail of High Availability
(abbreviated as HA). A few minutes downtime per year for mission
critical sites is acceptable. So, what is the state of technology?
A single, standalone server does not cut the HA mustard. You have
to have redundant hardware. Microsoft has created MS Cluster Server
for this (MSCS), and it does a good job at what it does, but it's
still early days. Failovers can sometimes be problematic or take
too long, and there is still a single point of failure, the shared
SCSI controller and drive.
Windows 2000 Advanced Server and Datacenter Server take the two
cluster nodes to 4, and have IP load balancing included. That builds
in more redundancy, but requires a *lot* of identical hardware and
For cost reasons, quite a few people choose for a 2-node MSCS and
buy an specific add-on product that makes MSCS into a great solution:
NSI's GeoCluster. Why? First of all, you do not need identical
hardware with GeoCluster. Second, you get rid of that last pesky
vulnerability of just one shared drive. GeoCluster allows you to
have each node its own storage! Third, failover goes *much* faster
as all the data is already on the second node. Once you have gone
through a four-hour Exchange fail-over you will understand why
this is important. [grin]
Last but not least, GeoCluster software allows you to create MSCS
clusters without the geographic limitations. It allows the two nodes
of a cluster to be broken out to a tested distance of 40KM but this
depends on the bandwidth and the quality of the line.
You can replicate continuously over a shared or private IP LAN, VLAN
or SAN IP connection. While standard MSCS clusters servers provide
protection against server or application failure, GeoCluster adds data
redundancy and provides greater protection against geographic disasters.
If you want to test GeoCluster on your Microsoft Cluster Server.
and fill out the QUESTIONS ABOUT GEOCLUSTER form at the bottom. One
of our Reps will get in touch with you and help with the installation.
If you are in Europe, we'll send you a 3.5inch CD with the product.