Vector always performs large block I/Os to read data from the disk. Large I/Os are most efficient if the data for a single I/O is stored together. The block_size parameter in the vectorwise.conf configuration file identifies the size of the block (page). The default value is 512 KB.

Typical data warehouse queries scan through very large volumes of data. If subsequent data blocks have to be accessed then the most efficient way to retrieve the data is if the blocks are stored together on disk. This is particularly important for spinning disks, where the cost of moving the disk head is expensive and sequential I/O delivers at least two times greater throughput than random I/O. Vector uses the parameter group_size to control the number of blocks (pages) that are stored together. The default value is 8.

The parameters block_size and group_size cannot be changed after the database has been created. If you want to change these parameters after database creation you must unload, destroy, recreate, and then reload the database.