Michael Wu and Willy Zwaenepoel. envy: A non-volatile, main memory storage system. In Proc. of the Sixth International Conference on Architectural Support for Programming Languages and Operating Systems, San Jose, California, pages 86--97, 1994. This article was processed using the L A T E X macro package with LLNCS style  Home/Search   Document Not in Database   Summary   Related Articles   Check

....[4] tries to improve on metadata operations by so called soft updates basing on delayed writes on most file operations. Many existing or researched in memory file systems, for example Phoenix [3] are those that can be used in small diskless units such as battery powered PDAs. Wu proposed eNVy [14] a memory based file system, but it still takes advantage of disk, treating it as a rescue in case of metadata overflow or to protect against memory failures. Conquest, a disk persistent RAM hybrid file system presented by Wang [13] uses nonvolatile RAM as a final storage destination for metadata ....

M. Wu and W. Zwaenepoel. eNVy: a non-volatile, main memory storage system. SIGPLAN Notices, 29(11):86--97, November 1994. 33

....RAM storage, it is appropriate to consider whether existing file system designs are suitable in this new environment. The Conquest file system is designed to address these questions and to smooth the transition from diskbased to persistent RAM based storage. Unlike other memory file systems [21, 10, 43], Conquest provides an incremental solution that assumes more file system responsibility in core as memory prices decline. Unlike HeRMES [25] which deploys a relatively modest amount of persistent RAM to alleviate disk traffic, Conquest assumes an abundance of RAM to perform most file system ....

Wu M, Zwaenepoel W, eNVy: A Non-Volatile, Main Memory Storage System. Proceedings of the October 1994.

....this large asymmetry between read and write cost will likely affect the memory hierarchy design. Multiple writes might be buffered and aggregated into a single write to conserve power and delay. This approach is similar in nature to proposed non volatile memory system architectures, such as eNVy [16]. Non volatility: Using magnetic rather than electrical storage provides a number of potential benefits. Magnetic storage may be less vulnerable to atmospheric radiation sources (such as ionized neutrons and alpha particles) but its susceptibility to other noise sources, such as stray ....

M. Wu and W. Zwaenepoel. eNVy: A non-volatile, main memory storage system. In Proceedings of the 6th Symposium on Architectural Support for Programming Languages and Operating Systems, pages 86-97, Oct 1994.

....is that MEMS devices have a much faster transition between active and inactive modes about 0.5 ms, as compared to several seconds in a traditional disk drive. Power conservation strategies for disk drives such as adaptive spin down [9, 10, 12] caching [2] and nonvolatile solid state memory [2, 22] have proven useful in reducing power consumption. Some of these schemes may not be applicable to MEMS storage devices due to the distinctive MEMS features, while others such as caching may be used to further reduce power consumption regardless of the secondary storage device. Additionally, new ....

M. Wu and W. Zwaenepoel. eNVy: a non-volatile, main memory storage system. In Proceedings of the 6th Interational Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), pages 86--97. ACM, Oct. 1994.

....overhead associated with writing to disks. Existing cluster failover schemes have high worst case recomputation costs, which is determined by the checkpoint interval time. Another line of related research is in the area of nonvolatile and persistent memory. For example, the eNVy system [38] uses non volatile Flash RAM to serve as a permanent data repository. It can tolerate hardware faults such as power outages. The Rio le cache [15] makes ordinary main memory safe for persistent storage by enabling memory to survive machine crashes. The main advantage of using non volatile or ....

Michael Wu and Willy Zwaenepoel. eNVy: A Non-Volatile, Main Memory Storage System. In ASPLOS'94. 11

....a block before it can be rewritten. The erase operation takes a few tens of milliseconds and can either be performed when a write to the block is required, or it can be decoupled from the write. The overhead due to the erase operation is called the cleaning overhead. Douglis et al. 94a] and [Wu Zwaenepoel 94] explored using flash memory as an alternative for disks. Douglis et al. 94a] compared the power and performance characteristics of hard disks versus two organizations of flash memory (a coupled write erase organization with small erase units and a decoupled write erase organizations with ....

....consumption and response time of the flash memory is strongly dependent on the amount of free flash space available. Energy consumption and response time suffered slightly until utilization reached 80 , then degrades very quickly beyond that, mainly due to the cost of cleaning the flash array. Wu Zwaenepoel 94] proposes a directly addressable flash storage system called eNVy. In their architecture, the system presents logical addresses to eNVy which maps it into physical addresses corresponding to banks of flash memory and battery backed SRAM. They use a small amount of battery backed SRAM to buffer ....

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Wu, M. and Zwaenepoel, W. eNVy: A Non-Volatile, Main Memory Storage System. In Proceedings of the Sixth International Conference on Architectural Support for Programming Languages and Operating Systems, pages 86--97, October 1994. 27

....not provide the same write bandwidth as disk, especially if erases cannot be done concurrently. There are a number of applications where Flash can be used in general purpose computers. It can be used as a replacement for (or extension of) main memory. For example, Wu and Zwaenepoel s system, eNVy [16], uses extensive amounts of Flash hardware to present Flashbased memory with in place update semantics. Flash may also be exploited for its persistence and low latency writes as a replacement for disk. Kawaguchi, Nishioka, and Motoda [4] have looked at implementing a Flash1 based file system, and ....

....of parallelism. Figure 1 illustrates a parallel bank of four 28F016SV chips that presents a 32 bit wide interface to 8 megabytes of Flash; write and erase bandwidths are increased four fold from single chip levels. In fact, much greater levels of parallelism are not unreasonable; the eNVy system [16] implements 256 way parallel Flash banks. This performance improvement comes at a higher total cost and reduced flexibility. Because data is striped across the chips, the effective minimum eraseable amount of Flash is increased. This defines what we shall call a Flash segment. In the 4 way case, ....

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M. Wu and W. Zwaenepoel. eNVy: A NonVolatile, Main Memory Storage System. In Proc. 6th International Conference oa Architectural Support for Programming Languages and Operating Systems, 1994. 15

....have been able to take advantage of customized replacement policies to enforce consistency. Further, this structure would have allowed RPVM to present a flexible memory management interface to its clients, if appropriate. 13 2.6. 2 Hybrid hardware software persistent memory The eNVy system [Wu Zwaenepoel 94] investigates the use of Flash RAM for implementing a fully persistent memory system. Flash memory is much easier to manufacture than DRAM, and is expected to approach the price capacity ratio of hard disks. In addition, Flash requires no power to maintain its contents. On the other hand, Flash ....

Michael Wu and Willy Zwaenepoel. eNVy: A Non-Volatile, Main Memory Storage System. In Proceedings of the 6th International Conference on Architectural Support for Programming Languages and Operating Systems, San Jose, California, October 1994.

.... utilization: picking the next segment by finding the one with the lowest utilization (i.e. the highest amount of memory that is reusable) MFFS uses this approach [4] More complicated metrics are possible; for example, eNVy considers both utilization and locality when cleaning flash memory [24]. The second aspect to erasure is performance. The SunDisk SDP flash disks couple erasure with writes, achieving a write bandwidth of 75 Kbytes s. The time to erase and write a block is dominated by the erasure cost. The Intel flash card separates erasure from writing, and achieves a write ....

....SDP5, but much worse write performance than a Caviar Ultralite CU140 or KH with an SRAM write buffer. This latter discrepancy suggests that an SRAM write buffer is appropriate for flash memory as well, something that we have not explored so far but that is an integral part of the eNVy architecture [24]. When using the numbers for measured performance as input to the simulator, the flash card does not perform as well as the flash disk. In particular, its write performance is worse than the simulated write performance based on the SunDisk SDP10, across all three traces. This discrepancy suggests ....

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Michael Wu and Willy Zwaenepoel. eNVy: a Non-Volatile, main memory storage system. In Proceedings of the Sixth International Conference on Architectural Support for Programming LanguagesandOperatingSystems, San Jose, CA, October 1994. To appear.

....not provide the same write bandwidth as disk, especially if erases cannot be done concurrently. There are a number of applications where Flash can be used in general purpose computers. It can be used as a replacement for (or extension of) main memory. For example, Wu and Zwaenepoel s system, eNVy [18], uses extensive amounts of Flash along with more limited amounts of SRAM to present Flash based memory with in place update semantics. Flash may also be used as a disk replacement. Kawaguchi, Nishioka, and Motoda [6] have looked at implementing a Flash based file system, and in a related work ....

....free pool Flash erase addr, num erases num segments of the Flash buffer starting at addr Flash recover persistent key maps in Flash associated with persistent key. Table 2: An operating system interface for Flash In fact, much greater levels of parallelism are not unreasonable; the eNVy system [18] implements 256 way parallel Flash banks. Because of striping, the effective minimum erasable amount of Flash is increased to the level of parallelism times the blocksize. This defines a Flash segment. In the 4 way case, these segments are 256 kilobytes, as illustrated in the Figure. In the ....

[Article contains additional citation context not shown here]

M. Wu and W. Zwaenepoel. eNVy: A Non-Volatile, Main Memory Storage System. In Proc. 6th International Conference oa Architectural Support for Programming Languages and Operating Systems, 1994.

....Systems and Software and is accepted for publications. # However, flash memory requires additional system support for erasure management because of the hardware characteristics [Caceres et al. 1993; Diper and Levy, 1993; Douglis et al. 1994; Intel, 1994; Intel, 1997; Kawaguchi et al. 1995; Wu and Zwaenepoel, 1994] shown in Table 1. Flash memory is partitioned into segments 2 defined by hardware manufacturers (e.g. 64 Kbytes or 128 Kbytes for Intel Series 2 Flash Memory Cards [Intel, 1994; Intel, 1997] and 512 bytes for SanDisk flash memory cards [SanDisk, 1993] Segments cannot be overwritten unless ....

.... a UNIX file system has such high locality that 67 78 of the writes are to metadata and most of the metadata updates are synchronous [Ruemmler and Wilkes, 1993] To avoid having to erase during every update, updates are not performed in place in many systems [Kawaguchi et al. 1995; Torelli, 1995; Wu and Zwaenepoel, 1994]. Data are updated to empty spaces in flash memory and obsolete data are left at the same place as garbage, which a software cleaning process later reclaims. The operations of cleaning process involve three stages as shown in Figure 2. The cleaning process first selects a victim segment and then ....

[Article contains additional citation context not shown here]

Wu, M., and Zwaenepoel, W., eNVy: A Non-Volatile, Main Memory Storage System, Proceedings of the 6th International Conference on Architectural Support for Programming Languages and Operating Systems (1994).

.... utilization: picking the next segment by finding the one with the lowest utilization (i.e. the highest amount of memory that is reusable) MFFS uses this approach [4] More complicated metrics are possible; for example, eNVy considers both utilization and locality when cleaning flash memory [24]. The second aspect to erasure is performance. The SunDisk sdp flash disks couple erasure with writes, achieving a write bandwidth of 75 Kbytes s. The time to erase and write a block is dominated by the erasure cost. The Intel flash card separates erasure from writing, and achieves a write ....

....sdp5, but much worse write performance than a Caviar Ultralite cu140 or kh with an SRAM write buffer. This latter discrepancy suggests that an SRAM write buffer is appropriate for flash memory as well, something that we have not explored so far but that is an integral part of the eNVy architecture [24]. When using the numbers for measured performance as input to the simulator, the flash card does not perform as well as the flash disk. In particular, its write performance is worse than the simulated write performance based on the SunDisk sdp10, across all three traces. This discrepancy suggests ....

[Article contains additional citation context not shown here]

Michael Wu and Willy Zwaenepoel. eNVy: a Non-Volatile, main memory storage system. In Proceedings of the Sixth International Conference on Architectural Support for Programming Languages and Operating Systems, San Jose, CA, October 1994. To appear. Douglis, et al. OSDI 11/94 Storage Alternatives for Mobile Computers 17

....crashes [Tanenbaum95, page 146] Memory s vulnerability to power outages is easy to understand and fix. A 119 uninterruptible power supply can keep a system running long enough to dump memory to disk in the event of a power outage [APC96] or one can use non volatile memory such as Flash RAM [Wu94]. We do not consider power outages further in this paper. Memory s vulnerability to OS crashes is more challenging. Most people would feel nervous if their system crashed while the sole copy of important data was in memory, even if the power stayed on [DEC95, Tanenbaum95 page 146, Silberschatz94 ....

....a way to provide data breakpoints [Kessler90, Wahbe92] and fault isolation between software modules [Wahbe93] Other projects seek to improve the reliability of memory against hardware faults such as power outages and board failures. eNVy implements a memory board based on non volatile, flash RAM [Wu94]. eNVy uses copy on write, page remapping, and a small, battery backed, SRAM buffer to hide flash RAM s slow writes and bulk erases. The Durable Memory RS 6000 uses batteries, replicated processors, memory ECC, and alternate paths to tolerate a wide variety of hardware failures [Abbott94] ....

Michael Wu and Willy Zwaenepoel. eNVy: A Non-Volatile, Main Memory Storage System. In Proceedings of the 1994 International Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), October 1994.

....and operating system crashes [Tanenbaum95, page 146] Memory s vulnerability to power outages is straightforward to understand and fix. A simple solution is to add an uninterruptible power supply to the system. Another solution is to switch to a non volatile memory technology such as Flash RAM [Wu94]. We do not consider power outages further in this paper. Memory s vulnerability to OS crashes is less concrete. Most people would feel nervous if their system crashed while the sole copy of important data was in memory, even if the power stayed on [DEC95, Tanenbaum95 page 146, Silberschatz94 page ....

....provide data breakpoints [Kessler90, Wahbe92] and fault isolation between software modules [Wahbe93] Other projects seek to improve the reliability of memory against hardware faults such as power outages and board failures. eNVy implements a memory board based on flash RAM, which is non volatile [Wu94]. eNVy uses copy on write, page remapping, and a small, battery backed, SRAM buffer to hide flash RAM s slow writes and bulk erases. The Durable Memory RS 6000 uses batteries, replicated processors, memory ECC, and alternate paths to tolerate a wide variety of hardware failures [Abbott94] ....

Michael Wu and Willy Zwaenepoel. eNVy: A Non-Volatile, Main Memory Storage System. In Proceedings of the 1994 International Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), October 1994.

....as storing them on disk. The two main factors limiting the reliability of memory are power outages and software corruption. Options for protecting memory against power outages include uninterruptible power supplies and switching to an inherently non volatile memory technology such as Flash RAM [Wu94]. This paper focuses on protecting memory against software induced corruption, which can account for 2 3 of all system outages [Gray90] 2 Why Is Memory Less Reliable Than Disks If someone surveyed system administrators and asked them if they would trust the contents of memory after a system ....

....provide data breakpoints [Kessler90, Wahbe92] and fault isolation between software modules [Wahbe93] Other projects seek to improve the reliability of memory against hardware faults such as power outages and board failures. eNVy implements a memory board based on flash RAM, which is non volatile [Wu94]. eNVy uses copy on write, page remapping, and a small, battery backed, SRAM buffer to hide flash RAM s slow writes and bulk erases. The Durable Memory RS 6000 uses batteries, replicated processors, memory ECC, and alternate paths to tolerate a wide variety of hardware failures [Abbott94] ....

Michael Wu and Willy Zwaenepoel. eNVy: A Non-Volatile, Main Memory Storage System. In Proceedings of the 1994 International Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), October 1994.

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M. Wu and W. Zwaenepoel. eNVy: a non-volatile, main memory storage system. In Proceedings of the 6th International Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), pages 86--97. ACM, Oct. 1994.

No context found.

Michael Wu and Willy Zwaenepoel. envy: A non-volatile, main memory storage system. In Proc. of the Sixth International Conference on Architectural Support for Programming Languages and Operating Systems, San Jose, California, pages 86--97, 1994. This article was processed using the L A T E X macro package with LLNCS style

No context found.

M. Wu and W. Zwaenepoel. eNVy: A non-volatile, main memory storage system. In Proceedings of the Sixth International Conference on Architectural Support for Programming Languages and Operating Systems, pages 86-97, San Jose, California, Oct. 4-7, 1994. ACM SIGARCH, SIGOPS, SIGPLAN, and the IEEE Computer Society.

No context found.

Michael Wu and Willy Zwaenepoel. eNVy: A non-volatile, main memory storage system. In Proceedings of the Sixth International Conference on Architectural Support for Programming Languages and Operating Systems, pages 86--97, San Jose, California, October 4--7, 1994. ACM SIGARCH, SIGOPS, SIGPLAN, and the IEEE Computer Society.

No context found.

M. Wu and W. Zwaenepoel. eNVy: a non-volatile, main memory storage system. In Proceedings of the 6th International Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), pages 86--97. ACM, Oct. 1994.

No context found.

M. Wu and W. Zwaenepoel. eNVy: a non-volatile, main memory storage system. In Proceedings of the 6th Interational Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), pages 86--97. ACM, Oct. 1994.

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