Reliable adaptable Network RAM

Abstract

We present reliability solutions for adaptable network RAM systems running on general-purpose clusters. Network RAM allows nodes with over-committed memory to swap pages over the network, storing them in the idle RAM of other nodes and avoiding swapping to slow, local disk. An adaptable network RAM system adjusts the amount of RAM currently available for storing remotely swapped pages in response to changes in nodespsila local RAM usage. It is important that network RAM systems provide reliability for remotely swapped page data. Without reliability, a single node failure can result in failure of unrelated processes running on other nodes by losing their remotely swapped pages. Adaptable network RAM systems pose extra difficulties in providing reliability because each nodepsilas capacity for storing remotely swapped pages changes over time, and because pages may move from node to node in response to these changes. Our novel dynamic RAID-based reliability solutions use idle RAM for storing page and reliability data, avoiding using slow disk for reliability. They are designed to work with the adaptive nature of our network RAM system (Nswap), allowing page and reliability data to migrate from node to node and allowing pages to be added to or removed from different parity groups. Additionally, page recovery runs concurrently with cluster applications, so that cluster applications do not have to wait until all data from a failed node is recovered before resuming execution. We present results comparing Nswap to disk swapping for a set of benchmarks running on our gigabit cluster. Our results show that reliable Nswap is up to 32 times faster than swapping to disk, and that there is virtually no impact on the performance of applications as they run concurrently with page recovery.