Missing option for file compare / validation after sync

Posts: 3 · dzabler 27 Jun 2020, 02:27

There are three different option to compare:
File time and size, File content and File size. I expect that these options should be combinable as I saw this in a different tool.
The most useful for me is the “File Time and size” + “File content”. To do this I have to start two times the compare with different settings.
The combination “File content” includes always the “File size”. Therefore, it can be set automatically.
In addition, a compare after a sync is useful and will saved me a lot of time. I know there is an option to validate files after coping. However, this is different, because after copying a file the validation uses the cache of the OS/HDD/SSD. I like to read it from the device again.
Another advantage of the compare after the sync is that you can cancel the compare and the sync was done. With a compare the time is nearly doubled but the cancel leads to a not synced job.

Posts: 2451 · Plerry 27 Jun 2020, 13:27

... I know there is an option to validate files after coping. However, this is different, because after copying a file the validation uses the cache of the OS/HDD/SSD. I like to read it from the device again ...dzabler, 27 Jun 2020, 02:27

Apparently you found the VerifyCopiedFiles flag and are warned by its remark on potentially hidden corruption. (Also make sure you follow the link that is provided there).
Effectively, there is no possibility for FFS (or any other application) to force the just written file to be read from the device (here: disk or SSD).
The only way to flush all caches in the chain is to reboot all devices (here: computers/servers, possibly including proxy's) involved in the sync.
So, with its VerifyCopiedFiles flag set to True, FFS already does the very best it can do.

Posts: 1038 · therube 29 Jun 2020, 19:10

Effectively, there is no possibility for FFS (or any other application) to force the just written file to be read from the device (here: disk or SSD).

Why?
(And not like I know one way or the other, but...

How to flush the disk read cache under Windows?
How can I invalidate the file system cache?
Manually flushing write cache on Windows
[Sync v2.2 says, "Client: Windows Vista and higher". Have long had it on XP. Suppose it works there too. Sync.exe itself says, "Sync 2.2: Disk Flusher for Windows 9x/Me/NT/2K/XP".]

Actually benchmarking hash check programs would make a good, rather easy test for some of the ideas mentioned above. Background Hashing.)

Posts: 2451 · Plerry 30 Jun 2020, 09:06

Obviously, to the extent one has full control/access to lower level features there are possibilities.
However, often syncs are made to network or even cloud resources.
Normally these simply are configured as file server, without access to lower level functions, and often even managed by others. In all those cases, FFS can't flush caches anywhere in the chain, with only the local machine as a potential exception. Nor can any other software running locally .