Data is usually made available by two means: redundancy and reliability.
Effort has been made to buy reliable hardware. Top of the line SSD, motherboard, memory, CPU and power supplies are used in the server.
Data is made redundant by providing multiple on-line copies of data. This is achieved primarily through a RAID1 mirror and protects against bad sectors and disk failures.
At some point I should add a small UPS to protect against power outages and brown outs.