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原帖由 maoleitau 於 2019-12-3 01:25 PM 發表


仲有Checksum, 作用係要保證所儲存既野準確無訣, 以每8bit Data需要一個Check bit計, 每儲存1G野就要另外儲存120M Data, 佔比成12.5%, 呢個先係真正最大原因, 當然allocation table都有影響. ...
But parity bit is stored with the data so it wouldn’t explain the OP’s scenario



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原帖由 maoleitau 於 2019-12-4 10:16 AM 發表


最簡單例子係Tape, 以前2G Native, 實際最多比你儲1.7G, 個0.3G就係Checksum同Data Block之間既間隔
I don’t get what you are saying. Parity bits are not checksums, while you can carry an extra bit for parity, the bit is stored along with the data and is not stored separately with a preallocated space on disk. Checksums are used to generate unique cryptographic signatures based on contents of a file, and are just fix length strings that are not proportional to the size of the file. For example, md5sum output is 128bits regardless of the size of the input file. 



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原帖由 maoleitau 於 2019-12-4 10:16 AM 發表


最簡單例子係Tape, 以前2G Native, 實際最多比你儲1.7G, 個0.3G就係Checksum同Data Block之間既間隔
I think that’s different issue. 2GB drive having 1.7GB space is due to difference in base 2 representation of bits. 



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