I wanted to make sure that two HDs (a RAID5 array and its single disk backup, both external disks on USB3) were synchronized and have confirmation of their contents, so with root start I generated a single CRC file using the MD5 algorithm, then I copied the file to the root of the backup single disk and started the check.
Shortly after starting, TotalCommander started reporting errors of "WRONG CRC" and "UNABLE TO ACCESS FILE" (or something like that): obviously I checked manually and those files were both fully accessible and with correct CRC MD5, check done generating the single CRC and comparing it with the relative hash in the single file of the multiple CRCs and with the direct control of the content ("Compare by content ...").
I probably write a stupid thing, but it would seem to be missing some timeout control in the process or a timing too short for reading files on USB3 which in the case of wrong CRC does not verify the actual reading of the whole file before decreeing the error, situation that could also generate the error in the non-identification of the files.
In fact and fortunately, keeping the same conditions and having the synchronization of the two disks checked again using the "content control" of the "Synchronize folder ..." function, everything is synchronized, accessible and error-free.
I apologize, it's the installation of Win7 to have problems, I executed the synchronization and consistency control on another machine with Windows 10 and no error was detected.
I apologize for my bad English ..
