I was sitting in a datacentre in the arse end of nowhere the other day waiting for a machine to boot when I noticed that 4 drives were flashing their activity lights at the same time. The fact that these 4 drives were spread across 2 machines was really shiny. It meant that soemthing I had set up was obvioulsy working properly.
Each machine had 2 mirrored disks using software raid which accounts for 2 drives in one machine flashing at the same time. What made all 4 drives flash at the same time was drbd which is bascially network raid 1.
We are using drbd along with heartbeat to provide a HA solution for our database needs.
Anyway it felt good to realise that soemthing I had setup had a physical means to show it is working. Although it has to be said it felt quite good when I could just yank the power out of a machine and have the database failover nicely.