Methods, systems, and computer program products for preserving atomic writes using leaves and bitmaps

摘要

Methods, systems, and computer program products for preserving atomic writes to disk arrays are disclosed. According to one method, portions of a file are stored in paired locations on a disk array such that a first location of a location pair for a file portion stores scratch data for the file portion and a second portion of the location pair for the file portion stores valid data for the file portion. A bitmap is stored on the disk array. The bitmap has bits indicating whether valid data for each file portion resides in the first or the second location for its respective location pair. A write request to write data to a portion of the file being less than the entire file is received. The bitmap indicates that valid data for the portion of the file to be written to resides in a first memory location of one of the location pairs on the disk array. In response to the write request, the bitmap is copied to memory, the data for the portion of the file requested to be modified is copied from the first location of the one location pair to a second location of the one location pair on the disk array without copying the entire file and modifying the data in the second location based on the data to be written. The bitmap stored in memory is modified to indicate that valid data for the portion of the file resides in the second location of the one location pair and that scratch data for the portion of the file resides in the first location on the disk array. A request to save the modification is received, and, in response to the request to save the modified data, the bitmap stored on the disk array is replaced with the modified bitmap.