block level

block level

Reading and writing a disk at the physical level. The disk controller uses block level to read and write the disks that are directly attached internally in every user's computer and most servers. In a storage area network (SAN), where disks are in their own cabinets external to the servers, read/write access is also at the block level (see SAN). Using IP storage, block level access is extended via the IP protocol to very remote locations (see IP storage).

Block Level Vs. File Level
Users never deal with data at the block level; however, database and network administrators may require that type of low level management. Block level access enables them to stipulate where data are stored for performance issues.

The term is widely used to contrast this lower level, physical method with the higher level, or logical, "file level" or "file access." The operating system's file system keeps track of data in a directory of file and folder names. Access to data by an application is by file name and location within the file, which is translated into block level for physical reading and writing.

Although a separate unit with its own disks, a network attached storage (NAS) device uses file level access. Block level transfers in a SAN are faster than file level transfers in a NAS because there is no file system or network overhead. See SAN and NAS.

Blocks Are Also Logical
Modern drives maintain their own tables of good and bad sectors and remap requests on the fly. As a result, the physical block reads and writes are translated by the drive into actual sector reads and writes, making the block access more of a logical request, rather than 100% physical.