Profiling the code, the CRC32 is indeed the slow point. I rewrote CRC32 into Assembler but got no appreciable boost in performance, as the Delphi compiler is very good at optimizing code performance. This is a slow process when examining 30,000 to 50,000 files. Those with identical extensions are then each calculated for CRC32 and stored in the database. Those with different file extensions are skipped. The DB is indexed on file size and all identical-sized files are further examined. On the first pass, I keep track of all three file create/modified/accessed time stamps, the fully qualified file name, and the file size in the database. Each filespec is recorded in a TOPAZ (DB4) flat file database which is a source-code level toolbox for Delphi. Part of that app is a non-recursive file search that starts at the specified parent directory, then searches all child leafs below. Years ago, I wrote the same app in Delphi, but use CRC32 as the hashing tool. Kudos for publishing this method in Powershell. There has to be some kind of rigorous and careful and fool proof procedure.īut this stuff is good. There’s gotta be a better way but it’s not simply running some duplicate finder/eliminator software is it? I never delete anything and just keep buying hard drives. ![]() ![]() ![]() I very much would like a workable technique for this.Ĭurrently I have lapsed into the ‘redundancy’ mode: i.e. We make backups and then get interrupted before the whole task is complete – which can take a long time when using only ‘spare’ time – and with maybe as many as eight disks to work on, something greater than 10 Terabytes – and there we are during the process with now ‘extra’ duplicates created just for the sake of the exercise! Part of the problem is hinted at here where you caution to make backups before doing anything. Moving them is the same as deleting them to software that expects to find them there. ‘Organising’ meant collecting like files together in one place. Whatever it was I know I created a real hell for myself in the past by trying to organise files and eliminate duplicates. Which can destroy all your config.txt or similar in a flash. You have to be very careful, right?īlindly eliminating duplicates can wreck everything I think I have found in the past.īut that may have been because my duplicate elimination software was too simplistic – perhaps not checking file length, calling files ‘duplicates’ merely because they had the same name. But i also know from experience it is not a simple job fixing it. I’ve got big problems with duplicate files, I know. I won’t need any other sources for what I want to know, looks like. Enough there to keep me busy for the rest of my life. | Move-Item -Destination $targetDir -Force -Verbose | Out-GridView -Title "Select the file(s) to move to `"$targetDir`" directory." -PassThru ` Get-ChildItem -Path $srcDir -File -Recurse | Group -Property Length ` This is accomplished by the PowerShell commands below: $srcDir = "D:\ISO Files" In this way, the overall time of the command is significantly reduced. The trick is to only compute the hashes of files having the same length because we already know that files with different lengths can't be duplicates. Because the Length value is retrieved from the directory, no computation is required. ![]() You probably know the Length property of the Get-ChildItem PowerShell cmdlet. Find duplicate files based on length and hashĪ necessary condition for duplicate files is that their size must match, which means that files where the size does not match cannot be duplicates. In the next section, we further optimize this command. The command will therefore take ages to find duplicates when used against a directory with a large number of large files. The hash computation is a resource-intensive operation, and the aforementioned command computes it for each file, regardless of its size. It works well for a few small files, but you will run into trouble if the source directory contains many large files. The command has one serious flaw, though.
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