• Journal of the Korea Society of Computer and Information
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• v.17 no.9
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• pp.127-138
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• 2012

In this paper, we present a tool (named VMBootFailMonitor) to detect and analyze a failure of a VM boot creation caused by faults on virtual disks of a Xen-based VM. Also, we presents an architecture and detail analysis process of the virtual disk faults in our tool. Especially, VMBootFailMonitor provides a causual analysis result for a case of VM creation failure based on three modules which performs virtual disk analysis, virtualized system analysis and system log analysis. We also support a comparison result between boot times of normal VMs and fault detection times of VM creation based on abnormal virtual disks. At result, our tool detects VM boot failures (3~6 seconds) within normal VM boot times (8~16 seconds).

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.3
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• pp.172-183
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• 2010

Virtual memory systems (VM) reduce disk I/Os caused by page faults using page prefetching, which reads pages together with a desired page at a page fault in a single disk I/O. Operating systems including 4.4BSD attempt to prefetch as many pages as possible at a page fault regardless of page access patterns of applications. However, such an approach increases a disk access time taken to service a page fault when a high portion of the prefetched pages is not referenced. More seriously, the approach can cause the memory pollution, a problem that prefetched pages not to be accessed evict another pages that will be referenced soon. To solve these problems, we propose an adaptive page prefetching control scheme (APC), which periodically monitors access patterns of prefetched pages in a process unit. Such a pattern is represented as the ratio of referenced pages among prefetched ones before they are evicted from memory. Then APC uses the ratio to adjust the number of pages that 4.4BSD VM intends to prefetch at a page fault. Thus APC allows 4.4BSD VM to prefetch a proper number of pages to have a better effect on reducing disk I/Os, though page access patterns of an application vary in runtime. The experiment of our technique implemented in FreeBSD 6.2 shows that APC improves the execution times of SOR, SMM, and FFT benchmarks over 4.4BSD VM by up to 57%.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.6
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• pp.57-62
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• 2022

Recently, fast storage media such as phage-change memory (PCM) emerge, and memory management policies for slow disk storage need to be revisited. In this paper, we propose a new page replacement policy that makes use of PCM as a swap device of virtual memory systems. The proposed policy aims at reducing write traffic to the swap device as well as reducing the number of page faults pursued by traditional page replacement policies. This is because a write operation in PCM is slow and PCM has limited write endurances. Specifically, the proposed policy focuses on the reduction of page faults when the memory load of the system is high, but it aims at reducing write traffic to storage when free memory space is sufficient. Simulation experiments with various memory reference traces show that the proposed policy reduces write traffic to PCM without performance degradations.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.5_6
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• pp.232-238
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• 2003

Traditional operating systems use a virtual memory to provide users with a bigger memory than a physical memory. The virtual memory augments the insufficient physical memory by the swap device. Since disks are usually used as the swap device, the cost of a page fault is relatively high compared to the access cost of the physical memory. Recently, numerous papers have investigated the Network RAM in order to exploit the idle memory in the network instead of disks. Since today's distributed systems are interconnected with high-performance networks, the network latency is far smaller than the disk access latency In this paper we design and implement the Network RAM using block device driver on Linux. This is the first implementation of the Network RAM on Linux. We propose the new reliability method to recover the page when the other workstation's memory is damaged. The system using the Network RAM as the swap device reduces the execution time by 40.3% than the system using the disk as the swap device. The performance results suggest that the new reliability method that use the processor more efficiently has the similar execution time with others, but uses smaller server memory and generates less message traffic than others.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.2
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• pp.305-311
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• 2010

iATA (Internet Advanced Technology Attachment) is a block-level protocol developed to transfer ATA commands over TCP/IP network, as an alternative network storage solution to address insufficient storage problem in mobile devices. This paper employs RAID5 distributed storage servers concept into iATA, in which the idea behind is to combine several machines with relatively inexpensive disk drives into a server array that works as a single virtual storage device, thus increasing the reliability and speed of operations. In the case of one machine failed, the server array will not destroy immediately but able to function in a degradation mode. Meanwhile, information can be easily recovered by using boolean exclusive OR (XOR) logical function with the bit information on the remaining machines. We perform I/O measurement and benchmark tool result indicates that additional fault tolerance feature does not delay read/write operations with reasonable file size ranged in 4KB-2MB, yet higher data integrity objective is achieved.