In computing (specifically data transmission and data storage), a block,[1] sometimes called a physical record, is a sequence of bytes or bits, usually containing some whole number of records, having a maximum length; a block size.
Some newer file systems, such as Btrfs and FreeBSD UFS2, attempt to solve this through techniques called block suballocation and tail merging.
The physical or logical volumes accessed via block I/O may be devices internal to a server, directly attached via SCSI or Fibre Channel, or distant devices accessed via a storage area network (SAN) using a protocol such as iSCSI, or AoE.
DBMSes often use their own block I/O for improved performance and recoverability as compared to layering the DBMS on top of a file system.
The stat command part of GNU Core Utilities can be used to check the block size.