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      Technical Aspects of Data: Volume, Velocity, Variation, Access, and Security

      GCP has a wide variety of data storage services. They are each designed to meet some use cases, but certainly not all of them. Earlier in the chapter, we considered data storage from a business perspective, and in this section, we will look into the more technical aspects of data storage. Some of the characteristics that you should keep in mind when choosing a storage technology are as follows:

      Knowing one of these characteristics will not likely determine the single storage technology you should use. However, a single mismatch between the data requirements and a storage service’s features can be enough to eliminate that service from consideration.

      Volume

      Some storage services are designed to store large volumes of data, including petabyte scales, whereas others are limited to smaller volumes.

Cloud Storage is an example of the former. An individual item in Cloud Storage can be up to 5 TB, and there is no limit to the number of read or write operations. Cloud Bigtable, which is used for telemetry data and large-volume analytic applications, can store up to 8 TB per node when using hard disk drives, and it can store up to 2.5 TB per node when using SSDs. Each Bigtable instance can have up to 1,000 tables. BigQuery, the managed data warehouse and analytics database, has no limit on the number of tables in a dataset, and it may have up to 4,000 partitions per table. Persistent disks, which can be attached to Compute Engine instances, can store up to 64 TB.

      Single MySQL First Generation instances are limited to storing 500 GB of data. Second Generation instances of MySQL, PostgreSQL, and SQL Server can store up to 30 TB per instance. In general, Cloud SQL is a good choice for applications that need a relational database and that serve requests in a single region.

      Velocity

      Velocity of data is the rate at which it is sent to and processed by an application. Web applications and mobile apps that collect and store human-entered data are typically low velocity, at least when measured by individual user. Machine-generated data, such IoT and time-series data, can be high velocity, especially when many different devices are generating data at short intervals of time. Here are some examples of various rates for low to high velocity:

      If data is ingested and written to storage, it is important to match the velocity of incoming data with the rate at which the data store can write data. For example, Bigtable is designed for high-velocity data and can write up to 10,000 rows per second using a 10-node cluster with SSDs. When high-velocity data is processed as it is ingested, it is a good practice to write the data to a Cloud Pub/Sub topic. The processing application can then use a pull subscription to read the data at a rate that it can sustain. Cloud Pub/Sub is a scalable, managed messaging service that scales automatically. Users do not have to provision resources or configure scaling parameters.

      At the other end of the velocity spectrum are low-velocity migrations or archiving operations. For example, an organization that uses the Transfer Appliance for large-scale migration may wait days before the data is available in Cloud Storage.

      Variation in Structure

Another key attribute to consider when choosing a storage technology is the amount of variation that you expect in the data structure. Some data structures have low variance. For example, a weather sensor that sends temperature, humidity, and pressure readings at regular time intervals has virtually no variation in the data structure. All data sent to the storage system will have those three measures unless there is an error, such as a lost network packet or corrupted data.

      Many business applications that use relational databases also have limited variation in data structure. For example, all customers have most attributes in common, such as name and address, but other business applications may have name suffixes, such as M.D. and Ph.D., stored in an additional field. In those cases, it is common to allow NULL values for attributes that may not be needed.

Not all business applications fit well into the rigid structure of strictly relational databases. NoSQL databases, such as MongoDB, CouchDB, and OrientDB, are examples of document databases. These databases use sets of key-value pairs to represent varying attributes. For example, instead of having a fixed set of attributes, like a relational database table, they include the attribute name along with the attribute value in the database (see Table 1.1).

Table 1.1 Example of structured, relational data