Janus: Optimal Flash Provisioning for Cloud Storage Workloads

Janus is a system for partitioning the flash storage tier
between workloads in a cloud-scale distributed file system
with two tiers, flash storage and disk. The file system
stores newly created files in the flash tier and moves them
to the disk tier using either a First-In-First-Out (FIFO)
policy or a Least-Recently-Used (LRU) policy, subject to
per-workload allocations. Janus constructs compact metrics
of the cacheability of the different workloads, using
sampled distributed traces because of the large scale of
the system. From these metrics, we formulate and solve
an optimization problem to determine the flash allocation
to workloads that maximizes the total reads sent to the
flash tier, subject to operator-set priorities and bounds on
flash write rates. Using measurements from production
workloads in multiple data centers using these recommendations,
as well as traces of other production workloads,
we show that the resulting allocation improves the
flash hit rate by 47–76% compared to a unified tier shared
by all workloads. Based on these results and an analysis
of several thousand production workloads, we conclude
that flash storage is a cost-effective complement to disks
in data centers.

Source: https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/41179.pdf


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