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65 lines
2.7 KiB
65 lines
2.7 KiB
2 years ago
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\page exodus_formats Exodus Formats
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\section large Large Model (64-bit offset)
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This is the current default format for exodus files. In this format,
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the size of an *individual* dataset within the file is limited
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to 4 GiB (2 GiB for older versions of netcdf library).
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Typically, the two largest datasets are an individual component of the
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nodal coordinates and the connectivity for an element block.
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An individual component of the nodal coordinates stored in double
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precision limits the model to about 2^29 (537 Million) nodes.
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The other dataset size is the connectivity of a single element
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block. For 8-node hexes, the maximum number of elements in an element
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block is 2^27 (134 Million) elements; for 27-node hexes, this is
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reduced to 39.7 million elements per element block.
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Since a complex model typically has many element blocks, the
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node count is typically the controlling dataset, but
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connectivity datasets can also be the limiting factor.
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Note that the model can typically split a large element block
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into two or more element blocks to avoid the connectivity
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limit, but there is no way to split the node coordinate
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dataset, so 2^29 is the hard upper limit on the number of
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nodes stored in a Large Model (64-bit offset) format exodus
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file.
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\section normal Normal, or Classic
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The non-transient portion of the model definition is limited to 2 GiB.
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This means that the size of the coordinates, connectivtity, nodeset,
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sideset, maps, and other datasets must total less than 2 GiB. This
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typically limits the model to about 35 million elements.
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This is no longer supported for writing by the exodus library, but old
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files in this format can still be read.
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\section nc4 Netcdf-4 Classic
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The netcdf-4 classic format uses HDF5 as the underlying file format
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on disk. This format eliminates the dataset size limits. However,
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since it only supports the use of 32-bit signed integers, the model
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is limited to 2^31 nodes and 2^31 elements.
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\section nc4nc Netcdf-4 Non-Classic
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This netcdf-4 non-classic format also uses HDF5 as the underlying
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file format on disk. There are no dataset size limits and it
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supports datasets storing 64-bit integers. With this format, the
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maximum model size should be unlimited. Models well in excess of 2
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Billion nodes and elements have been defined with this format
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verifying that the previous limits do not exist in this format.
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Currently when exodus uses this format, the only extension over the
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classic model is the use of 64-bit integers in some of the
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datasets. In the future, uses of additional netcdf-4 functionality
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(groups, compound datatypes) is planned.
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\section cdf5 CDF5
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A PNetCDF developed format which provides 64-bit integer capability
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in a non-HDF5-based file format. Being evaluated at this time.
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