posted 22 years ago
My $0.02
In that statement, the author does not really imply that VS will reduce Reliability / Scalability, perhaps the way to read it would be that VS will have little / no impact on Reliability and Availability, as compared with HS.
VS, as has been pointed out is achieved by adding processors / memory ...as opposed to HS, where new servers are added.
If you have just changed your server from a 2 processor m/c to a 4 processor m/c, how does that change availability / reliability? In multi-processor systems, the underlying OS is intelligent enough to spread its processing load amongst the processors. However if the disk array crashes, what difference will it make whether there were 2 or 4 processors? None. The m/c is down. Does both reliability and availability threats still exist even after VS.
As opposed to VS, in HS, new machines are added. You also either have specialized applications that can manage load or your software supports some kind of clustering and redundacy. In this example, if one server fails, the redundancy machanism will kick off and the system will continue to be available. Thus HS actually enhances the Reliability / Availability of a system.
HTH.
Sanjay Raghavan<br />SCJP2, SCEA-J2EE<br />Moderator - <a href="http://groups.yahoo.com/group/scea_prep" target="_blank" rel="nofollow">SCEA PREP</a><br />Co-Author - <a href="http://www.whizlabs.com/scea/scea.html" target="_blank" rel="nofollow">SCEA@Whiz</a><br /><i>Where did you sip your Java Today?</i>