What Is Block-Level Migration?

What is a block?

In block-level migrations, a block refers to a disk block. A disk block is the minimum logical unit for file systems to manage disk partitions. Disk blocks are similar to clusters in Windows. A block is also the minimum logic unit of disks used by OSs and software. The smallest unit for disk read or write is a sector. A sector is a physical area on a disk. The read and write operations to disk blocks are performed in sectors. Generally, a file is stored in several blocks, and one block maps to several physical sectors.

What is a block-level migration?

In block-level migrations, file systems are migrated by blocks. If the network is interrupted before the migration is complete, only impacted blocks need to be migrated again after the network recovers. If files are modified during the migration, only modified blocks need to be synchronized.

In file-level migrations, various tools like TAR are used for remote replication over SSH or other transmission protocols. If a file is modified during decompression or the network is interrupted before the migration is complete, the migration will fail. In addition, if a file is modified during the migration, the entire file needs to be synchronized. It means that all the blocks of the file must be synchronized. So, the synchronization efficiency is low.