Patent ID: 8239645

Claim:
A method for use in managing mirroring in data storage system having a fast write device and a slow write device, the method comprising: receiving a write I/O having a write data; executing the write I/O on the fast write device, the fast write device comprising a solid state drive; determining whether the write I/O may be aggregated into a sequential write request; based on negative determination, journaling the write I/O in a log stored on a journal LUN residing on the slow write device, wherein the slow write device resides on one or more conventional hard disks and represents at least part of a disk in the data storage system; based on positive determination, completing the write I/O by executing the write I/O on a mirror LUN residing on the slow write device after the write I/O is executed on the fast write device; indicating, after the write I/O is journaled, that execution of the write I/O is complete; and based on the journaling of the write I/O in the log, executing in background the write I/O journaled in the log to the mirror LUN, wherein mirroring is provided for the write data by maintaining first and second copies of the write data so that subsequent read I/O directed to the write data can be serviced from at least one of the fast write device and the mirror LUN residing on the slow write device, wherein the first copy of the write data resides on the fast write device and the second copy of the write data resides on the mirror LUN residing on the slow write device, wherein in the case of a failure of the fast write device, the write data of the fast write device is rebuilt from the mirror LUN residing on the slow write device aided as necessary by the log.