Ann W. Harrison wrote:

>The reason for my question is MySQL's "cluster" support.
>My reading of it is that their "clusters" have nothing to
>do with what used to be called clusters - groups of
>machines that share disk but not memory. The MySQL site
>claims that their clusters give "high availability" aka
>"5 nines". Looking more closely, "5 nines" means 99.999%
>up time. Sounds good. 0.001% of a week is 10 minutes.
>
>
>Regards,
>
>
>Ann
>
>

I always wonder about availability.

I think the time should be measured against use time (90% of my users
use my app in business hours), so to reach a full week I need 3 weeks
(taking as base 8 working hours a day).

For sure FB stays up more than 3 week without a downtime.

The only downtime I have is to update the DB when metadata change is
needed (wich is not a frequent task, 2 or 3 times per year).

My customers are small business (up to 25 client machines), but they run
on cheap servers (some places it even is shared with file sharing
services, I know it is not good, but for the customer is ok the
performance, etc. so he doesn't spend money in a extra server)

When a site rum 24x7 maybe 10 minutes of downtime could be reached
without to much difficulty, because anything that needs exclusive access
will shows up as a downtime. But in an evironment that has up to 20X7
(some hours of no users using the system) the system will have a 100%
uptime from the user point of view.

If I would say from my application's user's point of view, FB has far
more then 99.999% availability.

see you !

--

Alexandre Benson Smith
Development
THOR Software e Comercial Ltda.
Santo Andre - Sao Paulo - Brazil
www.thorsoftware.com.br