Write twice disk buffering

Non-volatile (safe) disk buffers improve performance in DBMSs. Writes to the disk buffer are durable without incurring physical disk writes. Moreover, physical writes at the disk can be performed at low cost using write piggybacking and multiblock purges. However, safe disk buffers are expensive. In this paper, unsafe buffers are used to simulate safe buffers, by writing each block twice to disk. The first write is performed immediately, anywhere. The second write is deferred, but written at a fixed location. These two writes together cost less than a single random write