Dbspace and chunk guidelines

This topic lists some general strategies for disk layout that do not require any information about the characteristics of a particular database.

  • Associate disk partitions with chunks and allocate at least one additional chunk for the root dbspace.
    A disk that is already partitioned might require the use of offsets. For details, see Allocating raw disk space on UNIX.
    Tip: With the 4-terabyte maximum size of a chunk, you can avoid partitioning by assigning a chunk per disk drive.
  • Mirror critical dbspaces: the root dbspace, the dbspaces that contain the physical log and the logical-log files. Also mirror high-use databases and tables.

    You specify mirroring at the dbspace level. Mirroring is either on or off for all chunks belonging to a dbspace. Locate the primary and the mirrored dbspaces on different disks. Ideally, different controllers handle the different disks.

  • Spread temporary tables and sort files across multiple disks.

    To define several dbspaces for temporary tables and sort files, use onspaces -t. When you place these dbspaces on different disks and list them in the DBSPACETEMP configuration parameter, you can spread the I/O associated with temporary tables and sort files across multiple disks. For information about using the DBSPACETEMP configuration parameter or environment variable, see the chapter on configuration parameters in the HCL OneDB™ Administrator's Reference.

  • Keep the physical log in the root dbspace but move the logical logs from the root dbspace. However, if you plan to store the system catalogs in the root dbspace, move the physical log to another dbspace.

    For advice on where to store your logs, see Location of logical-log files. Also see Move logical-log files and Change the physical-log location and size.

  • To improve backup and restore performance:
    • Cluster system catalogs with the data that they track.
    • If you use ON-Bar to perform parallel backups to a high-speed tape drive, store the databases in several small dbspaces.

      For additional performance recommendations, see the HCL OneDB Backup and Restore Guide.