Data Objects and File Striping
In a traditional Unix disk file system, an inode data structure contains basic information about each file, such as where the data contained in the file is stored. The Lustre file system also uses inodes, but inodes on MDTs point to one or more OST objects associated with the file rather than to data blocks. These objects are implemented as files on the OSTs. When a client opens a file, the file open operation transfers a set of object pointers and their layout from the MDS to the client, so that the client can directly interact with the OSS node where the object is stored, allowing the client to perform I/O on the file without further communication with the MDS.
If only one OST object is associated with an MDT inode, that object contains all the data in the Lustre file. When more than one object is associated with a file, data in the file is “striped” across the objects similar to RAID 0. Striping a file over multiple objects provides significant performance benefits. When striping is used, the maximum file size is not limited by the size of a single target. Capacity and aggregate I/O bandwidth scale with the number of OSTs a file is striped over. Also, since the locking of each object is managed independently for each OST, adding more stripes (one per OST) scales the file I/O locking capability of the filesystem proportionately. Each file in the filesystem can have a different striping layout, so that performance and capacity can be tuned optimally for each file.
Read more about this topic: Lustre (file System)
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