Using extents of indirect blocks for file mapping of large files

A method of operating a file server, the file server having data storage storing a file system, a data processor coupled to the data storage for access to files in the file system, and non-transitory computer readable storage medium coupled to the data processor and storing computer instructions, some of the files in the file system having file mapping metadata including an extent of contiguous indirect blocks, and some of the files in the file system having file mapping metadata including a tree of blocks, and the computer instructions, when executed by the data processor, perform a write operation to write data to a specified offset in a logical extent of a production file in the file system while maintaining a snapshot copy of the production file by the steps of:

• (a) accessing an indirect block in an extent of contiguous indirect blocks to read an ownership flag for the specified offset, and
• (b) in response to the ownership flag indicating that a data block for the specified offset is shared between the production file and the snapshot copy of the production file, writing data to a new data block for the production file, and changing the ownership flag to indicate that the data block for the specified offset is not shared between the production file and the snapshot copy of the production file, and extending a tree of blocks for file mapping of the data block that is no longer shared between the production file and the snapshot copy;
• wherein the extended tree of blocks includes some block pointers pointing to indirect blocks in the extent of contiguous indirect blocks, and other bock pointers pointing to indirect blocks in the extended tree of blocks, and each block pointer is in a respective block pointer field containing a respective flag indicating whether the block pointer in the block pointer field is pointing to either an indirect block in the extent of contiguous indirect blocks or a child block in the extended tree of blocks, and the flag is used to select either a first method for accessing a pointed-to indirect block in the extent of contiguous indirect blocks or a second method for accessing a pointed-to child block in the extended tree of blocks.

A file server comprising:

• data storage containing a file system;
• a data processor coupled to the data storage for access to files in the file system;
• and
• non-transitory computer readable storage medium coupled to the data processor and storing computer instructions, and
• each of the files having an inode containing file attributes including an indication of whether file mapping metadata of said each of the files includes either an extent of contiguous indirect blocks or a tree of blocks, so that some of the files in the file system are mapped by one or more extents of contiguous indirect blocks, and some of the files in the file system are mapped by one or more trees of blocks, and the computer instructions, when executed by the data processor, perform a read operation to read data from a specified offset in a logical extent of a specified file in the file system by the steps of:
• (a) reading the inode of the specified file to obtain an indication of whether the file is mapped at the specified offset by either an extent of contiguous indirect blocks or a tree of blocks, and
• (b) using the indication of whether the file is mapped at the specified offset by either an extent of contiguous indirect blocks or a tree of blocks to obtain, from the file mapping metadata, a pointer to a data block containing data at the specified offset of the specified file, and
• (c) using the pointer to read data to the data block for containing data at the specified offset in the logical extent of the specified file.