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Analysis of the Periodic Update Write Policy for Disk Cache
January 1992 (vol. 18 no. 1)
pp. 44-54

A disk cache is typically used in file systems to reduce average access time for data storage and retrieval. The 'periodic update' write policy, widely used in existing computer systems, is one in which dirty cache blocks are written to a disk on a periodic basis. The average response time for disk read requests when the periodic update write policy is used is determined. Read and write load, cache-hit ratio, and the disk scheduler's ability to reduce service time under load are incorporated in the analysis, leading to design criteria that can be used to decide among competing cache write policies. The main conclusion is that the bulk arrivals generated by the periodic update policy cause a traffic jam effect which results in severely degraded service. Effective use of the disk cache and disk scheduling can alleviate this problem, but only under a narrow range of operating conditions. Based on this conclusion, alternate write packages that retain the periodic update policy's advantages and provide uniformly better service are proposed.

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Index Terms:
periodic update write policy; file systems; average access time; data storage; computer systems; dirty cache blocks; average response time; disk read requests; cache-hit ratio; design criteria; competing cache write policies; bulk arrivals; traffic jam effect; degraded service; disk cache; disk scheduling; write packages; buffer storage; scheduling; storage allocation; storage management
S.D. Carson, S. Setia, "Analysis of the Periodic Update Write Policy for Disk Cache," IEEE Transactions on Software Engineering, vol. 18, no. 1, pp. 44-54, Jan. 1992, doi:10.1109/32.120315
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