Frequently-redundant array of independent disks

Abstract

There is provided a method and apparatus for effectuating data updates on a fault-tolerant storage device having a plurality of disk-drive units forming a disk array, with parity-block updates temporarily suspended to provide increased performance. Parity-block updates are typically deferred until the array is idle. Thus, data is written onto the array with no parity error correction information being present for a short amount of time. Data updates are effectuated by identifying the blocks in the array where data is to be written. New data is then written directly to the identified blocks without reading the old data present therein. A 'needs parity rebuild bit' (NPRB) is written to non-volatile memory, identifying the stripes not having parity information on the array. The number of NPRBs present is monitored to allow continuous calculation of a mean-time-to-data-loss (MTTDL). If the MTTDL is acceptable, parity updates are deferred until the array is idle. To that end, the I/O patterns to and from the array are monitored to determine idleness. If the I/O patterns indicate that the disk array is idle, new data is read and parity information is generated which is then written to the array.