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Dynamic iSCSI at Scale: Remote Paging at Google

Nick Black
Linux Plumbers Conference 2015


Google is experimenting with remotely mounting jobs’ binaries and data packages. Each package is served as an ext4 filesystem atop an iSCSI-mounted block device fed through dm-multipath and dm-verity. A typical job might run on O(1K) machines, employing a N-to-1 multipath configuration yielding O(10K) short-lived iSCSI sessions. Google thus sees O(100K) iSCSI sessions set up and torn down every minute, a rather atypical iSCSI deployment. We will explore the challenges presented by this deployment at scale.