To ensure a well performing server, you need to closely monitor three parameters:
1. Memory
2. CPU
3. Disk Space
You will notice also that hosts charge proportionally according to the above configurations.
Memory
Memory (RAM) monitoring is pretty simple as most operating systems have tools to show you how much RAM is in use. Because RAM is cheap and plentiful these days, it’s generally easy to make sure you have enough RAM. A lack of RAM causes slowdown and in extreme cases crashes applications could terminate due to lack of RAM. But in 99% of cases a lack of RAM means your system will be slow.
CPU
The CPU, being the heart of the computer, is a critical component to watch. Watching a CPU monitor is a lot like watching your car’s rev counter – if the rev counter is high then the machine is working hard. Do not under budget on CPU, as it will have a detrimental impact on the entire service. Too little CPU will never cause a system to crash, but a marked slowdown or intermittent service can be expected if your CPU starts to flat-line.
Disk Space
Disk drives come in magnetic and SSD versions. Magnetic is cheap, but there is a huge performance sacrifice compared to SSD. SSD drives can be from 5 to 20 times faster than magnetic drives. Disk space is more about sizing and your backup strategy. The beauty of a modern VPS is you can increase disk space on demand, whereas physical hardware requires downtime and hardware skills when upgrading disks. The key with magnetic disks is to project your needs two to five years in advance and size the disk appropriately. It’s hard and sometimes risky to switch of a long running mission critical server computer.