Tag Archives: fast

The Tail at Store: A Revelation from Millions of Hours of Disk and SSD Deployments

FAST '16 Mingzhe Hao, Gokul Soundararajan, Deepak Kenchammana-Hosekote, Andrew A. Chien and Haryadi S. Gunawi

14th USENIX Conference on File and Storage Technologies (FAST ’16)
Santa Clara, CA

We study storage performance in over 450,000 disks and 4,000 SSDs over 87 days for an overall total of 857 million (disk) and 7 million (SSD) drive hours. We find that storage performance instability is not uncommon: 0.2% of the time, a disk is more than 2x slower than its peer drives in the same RAID group (and 0.6% for SSD). As a consequence, disk and SSD-based RAIDs experience at least one slow drive (i.e., storage tail) 1.5% and 2.2% of the time. To understand the root causes, we correlate slowdowns with other metrics (workload I/O rate and size, drive event, age, and model). Overall, we find that the primary cause of slowdowns are the internal characteristics and idiosyncrasies of modern disk and SSD drives. We observe that storage tails can adversely impact RAID performance, motivating the design of tail-tolerant RAID. To the best of our knowledge, this work is the most extensive documentation of storage performance instability in the field.


ViewBox: Integrating Local File Systems with Cloud Storage Services

fast14Chris Dragga

Cloud-based file synchronization services have become enormously popular in recent years, both for their ability to synchronize files across multiple clients and for the automatic cloud backups they provide.

However, despite the excellent reliability that the cloud back-end provides, the loose coupling of these services and the local file system makes synchronized data more vulnerable than users might believe. Local corruption may be propagated to the cloud, polluting all copies on other devices, and a crash or untimely shutdown may lead to inconsistency between a local file and its cloud copy. Even without these failures, these services cannot provide causal consistency.

To address these problems, we present ViewBox, an integrated synchronization service and local file system that provides freedom from data corruption and inconsistency. ViewBox detects these problems using ext4-cksum, a modified version of ext4, and recovers from them using a user-level daemon, cloud helper, to fetch correct data from the cloud. To provide a stable basis for recovery, ViewBox employs the view manager on top of ext4-cksum. The view manager creates and exposes views, consistent in-memory snapshots of the file system, which the synchronization client then uploads. Our experiments show that ViewBox detects and recovers from both corruption and inconsistency, while incurring minimal overhead.

In Proceedings of the 12th USENIX Conference on File and Storage Technologies (FAST’14)