Block-Level Migration of SMS

In block-level migrations, a block refers to a disk block. A disk block is the minimum logical unit of the file system for managing 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 the 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.

In block-level migrations, the file system is migrated by blocks. Therefore, if the network is interrupted during the migration, only impacted blocks need to be migrated again after the network is recovered. If files are modified during the migration, only modified blocks need to be synchronized after the migration. In file-level migrations, various tools like TAR and SSH or other transmission protocols are used for remote replication. Therefore, if the file is changed during decompression or the network is interrupted during migration, the migration fails. In addition, if the file is changed during incremental data synchronization, the file needs to be synchronized again. In this case, all the blocks of the file must be synchronized. So, the synchronization efficiency is low. Block-level migration of file systems can better meet the incremental data synchronization requirements of SAP databases.

For more information about SMS, see Server Migration Service User Guide.