Disks and arrays.
WHAT TYPES EXIST
Mechanical drives: high capacity, lower cost, slower
Solid-state drives: far faster, more expensive per unit
High-performance solid-state, connected directly for maximum speed
WHAT DETERMINES CHOICE
Whether the workload is limited by capacity or by speed.
WHAT MOST WORKLOADS ARE LIMITED BY
Storage speed, more often than anything else.
WHAT THAT MEANS
Moving from mechanical to solid-state storage transforms most systems.
WHAT ARRAYS DO
Combine several drives for capacity, performance, resilience, or a combination.
WHAT THE COMMON ARRANGEMENTS PROVIDE
Mirroring: a complete copy, surviving one failure
Striping with parity: capacity with resilience to one or two failures
Combinations, balancing both
WHAT ARRAYS DO NOT PROVIDE
A backup.
WHY
They protect against drive failure, not deletion, corruption or disaster.
WHAT TO PLAN
Backups, regardless of array configuration.
WHAT TO MONITOR
Drive health and array status.
WHY
A degraded array with an unreplaced failed drive is one failure from total loss.
