15.00 - Repairing Cylinders - Teradata Database

Teradata Database Support Utilities

Teradata Database

Repairing Cylinders

Using Filer to make repairs to certain areas of the file system requires knowledge of data structures related to the Teradata File System. Teradata Database allocates cylinders for data storage of two basic types:

  • Normal cylinders are used for most file system storage, including PERM, SPOOL, JOURNAL, and WAL.
  • Normal cylinders can be of two fixed sizes:

  • Small cylinders each have 3872 sectors. Each sector is 512 bytes. Therefore a small cylinder is nearly 2 MB.
  • On systems that have been initialized to use large cylinders, small cylinders are still used to store WAL and DEPOT data.

  • Large cylinders are the size of six small cylinders, nearly 12 MB.
  • On systems that have been initialized to use large cylinders, large cylinders store all data types except WAL and DEPOT.

    Note: For 4 KB storage devices, Teradata Database treats 4 KB sectors as eight contiguous 512 byte sectors.

  • Durable cylinders are used to store certain special file system objects, such as the master index (MI) and file trace buffer (FTR). These are called “durable structures” because, after they are created in the file system, they persist. Unlike normal cylinders, durable cylinders are never freed back into general storage.
  • Teradata Database employs a directory structure known as the cylinder map. The map stores a list of all cylinders (small, large, and durable) on the system. Although it is unlikely, if one or more entries in the map becomes corrupted, Teradata Database cannot properly identify the corresponding cylinder types or whether they are large or small cylinders. For example, a durable cylinder can appear to the file system incorrectly as a set of normal cylinders with invalid data, or a set of contiguous small cylinders can appear a single large non-durable cylinder. Such situations result in file system errors.

    Use the following approaches to repairing such problems, depending on the nature of the problem:

  • If a durable cylinders is misidentified as a set of normal small cylinders, the simplest method of repair is to reallocate the durable structure, using the REALLOCDUR command. The normal cylinder sized portions of storage that had been part of the durable cylinder before reallocation can be returned to the pool of general cylinder storage using the QUARLIST /R, BADLIST /R, ASSIGN, or INIT command.
  • Alternatively, an attempt can be made to manually repair the first CI of the durable structure that was corrupted, such that it will again be recognized as a durable cylinder. Once the CI has been repaired, use the REBUILDMAP command to force the Teradata Database File System to again recognize the durable cylinder.

  • When a set of normal small cylinders is misidentified as a large (non-durable) cylinder, either use the ASSIGN command with the BREAKUP option, or use the PATCH command to appropriate size the first CI of the cylinder set.
  • In either case, quit and restart Filer after the repairs. This restarts the file system with the newly repaired CIs, which allows verification of the repairs.

    For more information on Filer commands related to cylinder repair, see “ASSIGN” on page 103, “BADLIST” on page 107, “INIT” on page 141, “PATCH” on page 166, “QUARLIST” on page 174, “REALLOCDUR” on page 178, and “REBUILDMAP” on page 181.