![]() For the test 10.9 MB file, standard 10% redundancy resulted in a total file size of 13.5 MB, rising to 16.4 MB for 30% redundancy.īecause Vandal inflicts random corruption throughout a file, recoverability using ECC varies slightly at any given level of corruption. There’s an initial overhead of about 10% for using any Parchive Par2 ECC, on top of which total file size rises linearly. Increasing levels of redundancy result in greater total file size, with more ‘parity’ data being stored in more. This has been corrupted using Vandal to a level of 45 B/MB, from which MacPAR deLuxe was able to completely recover the original image.Ĭorrupted at 46 B/MB, MacPAR deLuxe was unable to recover this original image, though. To illustrate the effect of corruption created by Vandal, here are three copies of the same HEIC image at different levels of corruption. That doesn’t indicate the percentage of corruption which can be corrected, but the amount of redundant repair information stored in the. There is one relevant control in the app: the “level of redundancy” used when creating. ![]() When repair can be completed to restore the expected checksums, the app writes the original uncorrupted document when attempts to repair are unsuccessful, the app reports that and all files are left unaltered. When the original file has been corrupted by Vandal, it fails some of the checksum tests and MacPAR deLuxe attempts to repair it using ‘parity’ data stored in the. par2 files aren’t required to do this, merely to confirm that the file’s checksums are correct. par2 files which are used together with the original file to try to reconstruct the original. MacPAR deLuxe was used to produce a Parchive in Par2 format, a folder of. As the file corruption technique, ECC and assessment are independent of file type, the conclusions should apply to any file, although some corrupted files are easier to use or repair when they’re still corrupted. Other test files included PDFs and one HEIC generated by the camera in an iPhone. The most frequently used test file was the SpringerOpen title Error-Correction Coding and Decoding, which I though might be appropriate, and is 10.9 MB in size. Files were corrupted using my utility Vandal, which overwrites individual bytes at randomly-selected locations within the file with random bytes, to achieve an even corruption rate which can be set from 1 B/MB upwards to over 500,000 B/MB. To run these tests, I used a selection of regular documents on my iMac Pro running Catalina 10.15.4. This article evaluates how effective that ECC is in practice. Last week I discovered that there is ECC available for all Macs in the Par2 or Parchive format, provided in Gerard Putter’s free utility MacPAR deLuxe. ![]() There are two effective strategies for preserving the integrity of important files: make multiple copies, and store them with error-correcting code (ECC) which will enable their recovery if and when they become damaged or corrupted. ![]()
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