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When the Docker service runs for the first time in the Docker server, a defined quantity of data space and metadata space is allocated from the Docker volume, using which data can be stored in the Docker container outside of the boot volume (but within the root file system). By default, the Docker offers thin provisioning facility of volumes which means that you have a big pool of available storage blocks within the volume and can create block devices such as virtual disks, of arbitrary size from that pool. The storage blocks will be marked as used or taken from the pool only when you actually write to it. The storage blocks are mapped to the data space and the metadata space for storage needs. Here, the Docker images are stored in the data space and the definite data about the docker images are stored in the metadata space. Since the Docker images are the basic building blocks of the Docker, if the data space or the metadata space is not sufficient, then new images and new containers based on the images cannot be created. If sufficient images are not available, then users cannot create new containers and simultaneously applications will also become inaccessible or the users will have only a limited choice of applications. To avoid such eventualities, it is inevitable that the data space and metadata space be monitored at regular intervals. The DockInfoTest test helps you in this regard!

This test reports the utilization of data and metadata space within a Docker server and proactively alerts administrators to potential space crunch, if any.

This test will run only if the Docker server is installed with the Device Mapper, which is a Linux kernel's framework for mapping physical block devices onto higher-level virtual block devices.

Outputs of the test : One set of results for the Docker server being monitored

Measurement	Description	Measurement Unit	Interpretation
data_used	Indicates the amount of data space currently utilized by this server.	GB	A low value is desired for this measure. If the value of this measure is closer to the Data space total measure, then it indicates that the Docker server is currently running short of space. Administrators have to ensure that sufficient data space is allocated to the Docker server.
data_total	Indicates the total amount of data space allocated to this server.	GB	Ideally, value of this measure should be low.
perc_dt_used	Indicates the percentage of data space utilized by this server.	Percent	A high value for this measure indicates that the Docker server is currently running out of space.
metadata_used	Indicates the amount of metadata space currently utilized by this server.	GB	Metadata is data that describes other data. Meta is a prefix that in most information technology usages means “an underlying definition or description”. Metadata summarizes basic information about data, which can make finding and working with particular instances of data easier. For example, author, date created and date modified and file size are examples of very basic document metadata. Having the ability to filter through that metadata makes it much easier for someone to locate a specific document. In addition to document files, metadata is used for images, videos, spreadsheets and web pages. The use of metadata on web pages can be very important. Metadata for web pages contain descriptions of the page's contents, as well as keywords linked to the content. These are usually expressed in the form of metatags.
metadata_total	Indicates the total amount of metadata space allocated to this server.	GB
perc_mt_used	Indicates the percentage of metadata space utilized by this server.	Percent	A low value is desired for this measure.