The Write Anywhere File Layout (WAFL) is a proprietary file system that supports large, high-performance RAID arrays, quick restarts without lengthy consistency checks in the event of a crash or power failure, and growing the filesystems size quickly. It was designed by NetApp for use in its storage appliances like NetApp FAS, AFF, Cloud Volumes ONTAP and ONTAP Select. Its author claims that WAFL is not a file system, although it includes one. It tracks changes similarly to journaling file systems as logs (known as NVLOGs) in dedicated memory storage device non-volatile random access memory, referred to as NVRAM or NVMEM. WAFL provides mechanisms that enable a variety of file systems and technologies that want to access disk blocks. Design WAFL stores metadata, as well as data, in files; metadata, such as inodes and block maps indicating which blocks in the volume are allocated, are not stored in fixed locations in the file system. The top-level file in a volume is the inode file, which contains the inodes for all other files; the inode for the inode file itself, called the root inode, is stored in a block with a fixed location. An inode for a sufficiently small file contains the file's contents; otherwise, it contains a list of pointers to file data blocks or a list of pointers to indirect blocks containing lists of pointers to file data blocks, and so forth, with as many layers of indirect blocks as are necessary, forming a tree of blocks. All data and metadata blocks in the file system, other than the block containing the root inode, are stored in files in the file system. The root inode can thus be used to locate all of the blocks of all files other than the inode file. Main memory is used as a page cache for blocks from files. When a change is made to a block of a file, the copy in the page cache is updated and marked dirty, and the difference is logged in non-volatile memory in a log called the NVLOG. If the dirty block in the page cache is to be written to permanent storage, it is not rewritten to the block from which it was read; instead, a new block is allocated on permanent storage, the contents of the block are written to the new location, and the inode or indirect block that pointed to the block