block allocation

Block allocation: a file on disk blocks allocated to the documents needed to avoid a waste of storage space. However, expansion of documents, paper documents will cause the block is not continuous, resulting in excessive disk seek time.

             Each time the file extension, the block allocation algorithm on the need to write to file information block structure, which is meta-dada. meta-data and documents to always write storage devices, document changes in the operation have to wait until all the meta-data operations have been completed before,

             Therefore, meta-data of the whole operation will significantly reduce the file system performance.

     Expansion of distribution: to create documents, a series of one-time allocation for the block, when the file extension, also allocated a lot of pieces. meta-data included in the document creation, when the file size no more than the paper on the distribution of all block size, do not have to write meta-data, until the need for redistribution of documents when the block.

                 Group to expand distribution of a block allocation of the way, the SCSI devices to reduce the time to write data, in order to read documents with a good performance, but the documents were read, and a similar block allocation.

                 Documents the group or block block cluster (block cluster) is the size of the compiler determined at the time. The size of the cluster file system performance has greatly affected.

     Note: meta-data meta-information: the relevant information and documents, such as authority, the owner and to create, access or change the time, and so on.

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