storage pool

Storage pool refers to the combined storage capacity that is obtained by combining one or more storage devices. Storage devices can be anything from a very small disk drive to large arrays of disk drives (each containing 20-30 drives).

A storage pool is created to get a very large capacity of GBs/TBs/PBs available, from which users are provided the required amount of storage.

For example, one can combine 10 hard disk drives of 4TB each, totaling to 40TBs. Now, one can either directly use the 40TB as a single device or partition the space out to many smaller storage capacities such as 100GB, 1TB and so on from this 40TB and provide that access to different users.

A storage pool can be created even after a cluster/fabric has been created. For example, you can add several unused disks to the distributed filesystem at the same time, to form a new storage pool.

If a disk that is a part of a storage pool fails and needs to be replaced, all data located in the storage pool is lost, including the data that is stored on the other disks from the storage pool. The data reconstruction or re-replication takes more time than the time taken if the failing disk was the only disk in the storage pool.

When data is replicated, data is available from other copies in other storage pools.

When erasure coding is used, the missing data blocks are reconstructed from other blocks with the help of parity blocks. The data block reconstruction operation is resource-intensive and takes time. During the operation, the files that have missing blocks missing are not available. If an application tries to read such files will either be suspended or get an I/O error during the read operation. Large storage pools should be avoided for erasure coding, by using storage labels.