Re: Options for wide-area database?

> RAC over Wide Area Network requires block-based replication utilizing
> your Storage Technology. I NEVER saw blockbased storage replication
> over distances working at a satisfying degree. Storage companies
> advertise FibreChannel over IP ... will believe that when I see it.

That's true. Some kind of FC over distance solution is required. But for a 'metro' solution, high-power SFP/GBIC should be able to reach at least 40 km (maybe 80km)? Obviously a WDM box would help too. Some FC switches allow buffer credits to be borrowed for the 'extended' port and that will give enough throughput for distance within 120km.

> I used to work for a hardware manufacturer 3 years ago. All the
> technical people doing implementation went crazy when another sales
> guy sold a "Metro Cluster" (in fact RAC would need a hardware cluster
> as a basis) because it's not working (network latency)

We've been testing SAN over distance for quite some time in various areas (e.g. bulk transfer/mirroring, distributed filesystem), and we did some RAC over distance as well. On a distance extended SAN, we found that RAC is more sensitive with the private network latency than the latency at the SAN layer - we used independent distance emulation on the private link and SAN and we alter them independently to see the performance effect. It seems the cache fusion / heart-beat communication is very latency sensitive. However, within a metro environment (>100km) there's only about a > 1ms latency and we don't see that as a problem. Moreover, we have to extend/borrow the buffer credits on the WAN port. The usual setting only allows 100% thruput within 10km distance. Note that the testing we do are all on 2-nodes cluster.

> Consider using data guard but also consider third party products as
> data guard is not perfect either. If the database is not to big use
> Shareplex (heavy I/O as far as I know, usually not perfect with
> complex SAP environments) or think about other alternatives. A product
> called DBShadow is handling it pretty well, too.
>
> ... my opinion.

I'll take a look at those.... Thanks.

Ernest Received on Tue Feb 17 2004 - 12:37:46 CST