On Thursday, 09/30/2010 at 05:11 EDT, Alan Cox <[email protected]> wrote: > > Reliable HA is hard and a lot of work to get right. That's why products > > like IBM Tivoli Systems Automation for Multiplatform exist. > > Reliable full HA is also usually very expensive and it's easy to get > sucked into the 'and if we add this we get XX benefit' catalogue > shopping or sales spiel. > > Start with a risk assessment not a catalogue. If you don't know the cost > of a failure, a guess at fail rates or the expected recovery time without > HA you don't know how much you need to improve and what the justifiable > spend is. > > Sometimes a little bit of redesign to remove the HA requirement > from a system can be a lot cheaper than HA, often however with shared > consistent data it's not easy or not possible.
Absolutely. HA is a discipline all of its own that drags many technologies and policies with it. The Hierarchy of HA takes you all the way from customer access down to alternate power sources: - ISPs - Power - Switches and routers - Cables - OSA - DASD - LPARs & CECs - OSes and the Apps they run As you and Rob suggest, each has a value and a cost. It must be analyzed. Some things are cheaper to protect than others. It may make sense to spend $100K a year to protect $1M in revenue. It does not make sense to spend $1M to protect $100K. (That's the same discussion as Security.) That explains why companies are willing to accept fines rather than fix a problem. During the early design of z/VM Single System Image, there was much discussion on the value of virtual server mobility, ultimately coming to understand that it could not be a solution in and of itself, but would be another powerful tool in the HA toolbox. Necessary for some, but rarely sufficient. So know what the Problems are before you start implementing Solutions. Alan Altmark z/VM and Linux on System z Consultant IBM System Lab Services and Training ibm.com/systems/services/labservices office: 607.429.3323 [email protected] IBM Endicott ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
