The DEPOT command displays cylinder summary information for cylinders in the Depot, or block summary information for blocks in a particular Depot cylinder.
- The 64-bit identifier of a cylinder, entered as a 16-character hexadecimal number.
- Filer will use the most recently saved value for cylid.
- This option cannot be used unless an input value has already been defined for cylid. For more information, see Stored Input Values.
The Teradata Database File System stages in-place writes of permanent and system tables through a disk area called the Depot, which is a collection of cylinders. In-place modifications are first written to the Depot and only then written to their original Home Disk Address (HDA).
During system startup, the Depot is examined and any blocks that are found are read in, validated, and re-written to their original HDA. This ensures that any blocks that might have been partially written to their HDA, when a system outage occurred, can be rewritten as complete blocks. Handling writes this way greatly reduces the possibility of a partial-write scenario destroying pre-existing data. Any blocks partially written to the Depot will not pass validation, and thus will not overwrite the previous version of the block that still exists at the HDA.
Because a write to the Depot must be complete before the block is written to the HDA, an interruption can only corrupt one of the copies of the block. A failed write to the Depot can be recovered by applying the WAL log records to the copy of the block at the HDA. A failed write to the HDA can be recovered by copying the block in the Depot over the block at the HDA.
The Depot can contain both DBs and WDBs. The contents of the Depot may be different each time you view it since data is constantly moving in and out of the Depot.