weatherspoon - Smoke and Mirrors: Reecting Files at a...

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USENIX Association 7th USENIX Conference on File and Storage Technologies 211 Smoke and Mirrors: Reflecting Files at a Geographically Remote Location Without Loss of Performance Hakim Weatherspoon, Lakshmi Ganesh, Tudor Marian, Mahesh Balakrishnan, and Ken Birman Cornell University, Computer Science Department, Ithaca, NY 14853 {hweather,lakshmi,tudorm,ken} Microsoft Research, Silicon Valley Abstract The Smoke and Mirrors File System (SMFS) mirrors files at geographically remote datacenter locations with negligible impact on file system performance at the pri- mary site, and minimal degradation as a function of link latency. It accomplishes this goal using wide-area links that run at extremely high speeds, but have long round-trip-time latencies—a combination of properties that poses problems for traditional mirroring solutions. In addition to its raw speed, SMFS maintains good syn- chronization: should the primary site become completely unavailable, the system minimizes loss of work, even for applications that simultaneously update groups of files. We present the SMFS design, then evaluate the system on Emulab and the Cornell National Lambda Rail (NLR) Ring testbed. Intended applications include wide-area file sharing and remote backup for disaster recovery. 1 Introduction Securing data from large-scale disasters is important, es- pecially for critical enterprises such as major banks, bro- kerages, and other service providers. Data loss can be catastrophic for any company — Gartner estimates that 40% of enterprises that experience a disaster (e.g. loss of a site) go out of business within five years [41]. Data loss failure in a large bank can have much greater conse- quences with potentially global implications. Accordingly, many organizations are looking at dedi- cated high-speed optical links as a disaster tolerance op- tion: they hope to continuously mirror vital data at re- mote locations, ensuring safety from geographically lo- calized failures such as those caused by natural disas- ters or other calamities. However, taking advantage of this new capability in the wide-area has been a chal- lenge; existing mirroring solutions are highly latency sensitive [19]. As a result, many critical enterprises op- erate at risk of catastrophic data loss [22]. The central trade-off involves balancing safety against performance. So-called synchronous mirroring solu- tions [6, 12] block applications until data is safely mir- rored at the remote location: the primary site waits for an acknowledgment from the remote site before allow- ing the application to continue executing. These are very safe, but extremely sensitive to link latency. Semi- synchronous mirroring solutions [12, 42] allow the ap- plication to continue executing once data has been writ- ten to a local disk; the updates are transmitted as soon as possible, but data can still be lost if disaster strikes. The end of the spectrum is fully asynchronous: not only
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weatherspoon - Smoke and Mirrors: Reecting Files at a...

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