Basic Definitions
Latency: Latency is simply the time it takes to retrieve data.
Cache: Cache is an in-memory storage service.
SSDs: Solid State Drives
HDDs: Hard Disk Drives
Types of Storage Services offered by Cloud Providers
Object storage : manages data in terms of blobs or objects. Each object is individually addressable by a URL. While these objects are files, they are not stored in a conventional file system.
File storage : provides network shared file storage to VMs.
Block storage : uses a fixed size data structure called blocks to organize data. 4kb is the common block size for its file system. However, block sizes of 8kb are often used by relational databases that are designed to access block storage directly.
Caches : are in-memory data stores that maintain/provide fast access to data. The latency of in-memory stores is designed to be submillisecond making them the fastest data store after SSDs
Note: 1000 nanoseconds = 1microsecond
1000microseconds = 1millisecond
1000milliseconds = 1second
Reading 4KB randomly from an SSD takes 150 microseconds
Reading 1MB sequentially from cache memory takes 250 microseconds
Reading 1MB sequentially from an SSD takes 1,000 microseconds or 1 millisecond
Reading 1MB sequentially from disk (HDDs) takes 20,000 microseconds or 20 milliseconds,
Reading from disk takes 80 times longer than reading from an in-memory cache!