In a virtualization environment that serves multiple tenants (independent organizations), storage consolidation at the filesystem level is desirable because it enables data sharing, administration efficiency, and performance optimizations. The scalable deployment of filesystems in such environments is challenging due to intermediate translation layers required for networked file access or identity management. First we define the entities involved in a multitenant filesystem and present relevant security requirements. Then we introduce the design of the Dike authorization architecture. It combines native access control with tenant namespace isolation and compatibility to object-based filesystems. We introduce secure protocols to authenticate the participating entities and authorize the data access over the network. We alternatively use a local cluster and a public cloud to experimentally evaluate a Dike prototype implementation that we developed. At several thousand tenants, our prototype incurs limited performance overhead below 21 percent, unlike a solution from industry whose multitenancy overhead approaches 84 percent in some cases.

Hardware consolidation in the datacenter often leads to scalability bottlenecks from heavy utilization of critical resources, such as the storage and network bandwidth. Client-side caching on durable media is already applied at block level to reduce the storage backend load but has received criticism for added overhead, restricted sharing, and possible data loss at client crash. We introduce a journal to the kernel-level client of an object-based distributed filesystem to improve durability at high I/O performance and reduced shared resource utilization. Storage virtualization at the file interface achieves clear consistency semantics across data and metadata, supports native file sharing among clients, and provides flexible configuration of durable data staging at the host. Over a prototype that we have implemented, we experimentally quantify the performance and efficiency of the proposed Arion system in comparison to a production system. We run microbenchmarks and application-level workloads over a local cluster and a public cloud. We demonstrate reduced latency by 60% and improved performance up to 150% at reduced server network and disk bandwidth by 41% and 77%, respectively. The performance improvement reaches 92% for 16 relational databases as clients and gets as high as 11.3x with two key-value stores as clients.

In a virtualization environment that serves multiple tenants, storage consolidation at the filesystem level is desirable because it enables data sharing, administration efficiency, and performance optimizations. The scalable deployment of filesystems in such environments is challenging due to intermediate translation layers required for networked file access or identity management. First we present several security requirements in multitenant filesystems. Then we introduce the design of the Dike authorization architecture. It combines native access control with tenant namespace isolation and compatibility to object-based filesystems. We use a public cloud to experimentally evaluate a prototype implementation of Dike that we developed. At several thousand tenants, our prototype incurs limited performance overhead up to 16%, unlike an existing solution whose multitenancy overhead approaches 84% in some cases.

Synchronous small writes play a critical role in system availability because they safely log recent state modifications for fast recovery from crashes. Demanding systems typically dedicate separate devices to logging for adequate performance during normal operation and redundancy during state reconstruction. However, storage stacks enforce page-sized granularity in data transfers from memory to disk. Thus, they consume excessive storage bandwidth to handle small writes, which hurts performance. The problem becomes worse, as filesystems often handle multiple concurrent streams, which effectively generate random I/O traffic. In a journaled filesystem, we introduce wasteless journaling as a mount mode that coalesces synchronous concurrent small writes of data into full page-sized journal blocks. Additionally, we propose selective journaling to automatically activate wasteless journaling on data writes with size below a fixed threshold. We implemented a functional prototype of our design over a widely-used filesystem. Our modes are compared against existing methods using microbenchmarks and application-level workloads on stand-alone servers and a multitier networked system. We examine synchronous and asynchronous writes. Coalescing small data updates to the journal sequentially preserves filesystem consistency while it reduces consumed bandwidth up to several factors, decreases recovery time up to 22%, and lowers write latency up to orders of magnitude.