Re: Oracle 9i RAC vs Hardware clustering (like HACMP)

Praveen wrote:

> Hello,
>
> We are exploring the options of high availability. Harware clustering
> seems to be the first choice and using Oracle RAC on a hardware
> cluster would further enhance availability. But could anyone let me
> know the advantages of using Oracle RAC instead of plain hardware
> clustering such as HACMP.
>
> Thanks,
> Praveen

HACMP attempts to keep the CPU cycles up and available.

RAC keeps the database up and the data available. Regardless of what HACMP thinks it's doing. Even if there's no HACMP or other h/w cluster in sight.

Most cluster environments without RAC simply are designed to flop over to the alternate environment when something fails ... Flopping, however, requires the floppee to freshen up an bit before making an appearance.

In other words - RAC keeps the database up and available while the OS & application can switch over. Without RAC, the database's instance must undergo some form of restart to get loaded into the target machine's memory. That restart could involve a full instance recovery or worse and could take significant time (minutes to hours), even if the technical cluster failover happens near-subsecond.

While not entirely accurate, I'd prefer to equate HACMP to Oracle's DataGuard - can be automated, somewhat faster than needing to restart manually, and almost guaranteed to have all the needed structures around close by.

/Hans Received on Mon Oct 18 2004 - 14:50:04 CDT