Does Rio work for write-back CPU caches?
Yes. The key is getting the data from the CPU cache to memory before the CPU is reset. This is easy on our current Alpha platform (DEC 3000). The DEC 3000 provides a physical reset button that jumps to the console. A console (or boot) routine can flush the cache before rebooting. For PCs, the Rio port to FreeBSD uses a “safe sync” mechanism that flushes the data to disk during a crash. Safe sync is triggered from the low-level keyboard interrupt handler. We are validating and refining this method, but early measurements indicate this works for over 95% of crashes. • Does Rio provide reliability or availability? Rio’s focus is reliability (not losing data). In general, availability (being able to access data continuously) requires hardware replication. Rio can provide availability in much the same way that disks can. For example, a cheap serial line from the memory card to another computer would provide availability while rebooting or during hardware failure. With safe sync, Rio can pro
