MEMS-based storage devices promise significant performance, reliability, and power improvements relative to disk drives. this paper compares and contrasts these two storage technologies and explores how the physical c...
MEMS-based storage devices promise significant performance, reliability, and power improvements relative to disk drives. this paper compares and contrasts these two storage technologies and explores how the physical characteristics of MEMS-based storage devices change four aspects of operatingsystem (OS) management: request scheduling, data placement, failure management, and power conservation. Straightforward adaptations of existing disk request scheduling algorithms are found to be appropriate for MEMS-based storage devices. A new bipartite data placement scheme is shown to better match these devices' novel mechanical positioning characteristics. With aggressive internal redundancy, MEMS-based storage devices can mask and tolerate failure modes that halt operation or cause data loss for disks. In addition, MEMS-based storage devices simplify power management because the devices can be stopped and started rapidly.
this paper describes an asynchronous state-machine replication systemthat tolerates Byzantine faults, which can be caused by malicious attacks or software errors. Our system is the first to recover Byzantine-faulty r...
this paper describes an asynchronous state-machine replication systemthat tolerates Byzantine faults, which can be caused by malicious attacks or software errors. Our system is the first to recover Byzantine-faulty replicas proactively and it performs well because it uses symmetric rather than public-key cryptography for authentication. the recovery mechanism allows us to tolerate any number of faults over the lifetime of the system provided fewer than 1/3 of the replicas become faulty within a window of vulnerability that is small under normal conditions. the window may increase under a denial-of-service attack but we can detect and respond to such attacks. the paper presents results of experiments showing that overall performance is good and that even a small window of vulnerability has little impact on service latency.
Internet users increasingly rely on publicly available data for everything from software installation to investment decisions. Unfortunately, the vast majority of public content on the Internet comes with no integrity...
Internet users increasingly rely on publicly available data for everything from software installation to investment decisions. Unfortunately, the vast majority of public content on the Internet comes with no integrity or authenticity guarantees. this paper presents the self-certifying read-only file system, a content distribution system providing secure, scalable access to public, read-only *** read-only file system makes the security of published content independent from that of the distribution infrastructure. In a secure area (perhaps off-line), a publisher creates a digitally-signed database out of a file system's contents. the publisher then replicates the database on untrusted content-distribution servers, allowing for high availability. the read-only file system protocol furthermore pushes the cryptographic cost of content verification entirely onto clients, allowing servers to scale to a large number of clients. Measurements of an implementation show that an individual server running on a 550 Mhz Pentium III with FreeBSD can support 1,012 connections per second and 300 concurrent clients compiling a large software package.
Overcast is an application-level multicasting systemthat can be incrementally deployed using today's Internet infrastructure. these properties stem from Overcast's implementation as an overlay network. An ove...
Overcast is an application-level multicasting systemthat can be incrementally deployed using today's Internet infrastructure. these properties stem from Overcast's implementation as an overlay network. An overlay network consists of a collection of nodes placed at strategic locations in an existing network fabric. these nodes implement a network abstraction on top of the network provided by the underlying substrate *** provides scalable and reliable single-source multicast using a simple protocol for building efficient data distribution trees that adapt to changing network conditions. To support fast joins, Overcast implements a new protocol for efficiently tracking the global status of a changing distribution *** based on simulations confirm that Overcast provides its added functionality while performing competitively with IP Multicast. Simulations indicate that Overcast quickly builds bandwidth-efficient distribution trees that, compared to IP Multicast, provide 70%-100% of the total bandwidth possible, at a cost of somewhat less than twice the network load. In addition, Overcast adapts quickly to changes caused by the addition of new nodes or the failure of existing nodes without causing undue load on the multicast source.
systems software such as OS kernels, embedded systems, and libraries must obey many rules for both correctness and performance. Common examples include "accesses to variable A must be guarded by lock B," &qu...
systems software such as OS kernels, embedded systems, and libraries must obey many rules for both correctness and performance. Common examples include "accesses to variable A must be guarded by lock B," "system calls must check user pointers for validity before using them," and "message handlers should free their buffers as quickly as possible to allow greater parallelism." Unfortunately, adherence to these rules is largely *** paper attacks this problem by showing how system implementors can use meta-level compilation (MC) to write simple, system-specific compiler extensions that automatically check their code for rule violations. By melding domain-specific knowledge withthe automatic machinery of compilers, MC brings the benefits of language-level checking and optimizing to the higher, "meta" level of the systems implemented in these languages. this paper demonstrates the effectiveness of the MC approach by applying it to four complex, real systems: Linux, OpenBSD, the Xok exokernel, and the FLASH machine's embedded software. MC extensions found roughly 500 errors in these systems and led to numerous kernel patches. Most extensions were less than a hundred lines of code and written by implementors who had a limited understanding of the systems checked.
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