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AllocFS: A Filesystem With AllocationsSpace allocation is a critical facility for making reliable data intensive computing systems. However, traditional operating systems do not make it easy to guarantee that space will be available for a future operation.
To address this limitation, we have developed AllocFS, a filesystem that allows users to make guaranteed space allocations within an existing directory structure. For example, the user simply issues mkalloc /dir/name 25M and receives a directory that is guaranteed to hold 25MB of data. Allocations are hierarchical, so this space can be further divided for other purposes.
AllocFS is a modified version of the production ext2 filesystem. It is a loadable kernel module that uses the same on-disk layout as ext2, so the allocation facility can be added to (or removed from) an existing filesystem without reformatting.