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Backup to a 'Local Backup' device, may fail to backup selected objects, and backup log states warnings: "fat table not found, invalid document .." and "fct: could not locate channel in ..", due to at

Backup to a 'Local Backup' device (as the primary target device that the backup job uses, which could either be direct to 'Local Backup' device or a Hybrid enabled backup job, that always uses the 'Local Backup' device as the primary target device), may fail to backup either all or only a partial amount of the selected file objects (sometimes the backup log will state that there were no completed files, and other times it will only show a partial amount of completed files, it just depends), and the backup log states at least one (sometimes the backup log will show both, and other times only one) of these two warnings: "fat table not found, invalid document .." and "fct: could not locate channel in ..", due to at least one backup .dat file is bad or was partially written, etc. (or partial, like it was half written because it ran out of space) file. In that case there could be 1 of those .dat files like that present on the target 'Local Backup' device folder location, or there could be more than 1, but the filename itself will always be listed inside each "warning" text in the backup log in that case. This same warning text can also occur for Restores of backups as well, which if that is needed in your case, we have a seperate how-to KB article on that to read here. The 21.2.x client versions (that Step 1 deals with) have improved how the FPI backup engine will deal with partial or corrupt backup set .dat files (usually due to running out of space on the device), or if the expected .dat file to read from does not exist at all anymore, but that isn't always perfect, so these instructions have to exist for you to use. FYI, if the folder location that the 'Local Backup' device is assigned to use (as seen in the Device tab) is out of disk space, or very low, then this problem can occur that the backup .dat file will only be partially written (like only as a 0 byte file), that can certainly lead to this issue just know (that Step 2 deals with).

An example of the (FPI modern backup engine) backup job log warnings ("fat table not found, invalid document .." and "fct: could not locate channel in .." pair of two warnings, per .dat filename) text below; which only states a single "invalid document datafile" .dat file in the set of warnings (the same file is mentioned a total of 3 times in this backup log content text, but it is only for a single file keep in mind, but there could be more .dat files listed in your log to need to deal with), so in that case only one .dat file needs to be looked into to manually delete to fix this issue (as the backup engine can't delete that bad or partial .dat file for you, in any of the current 21.2.x client versions):

Instructions on how to correct this issue (manually) for backups that show the above set of two warnings:

  1. Make sure that the client version that you are running is 21.2.x, hopefully the latest client version in that case. If you are not on that version then you will need to upgrade the client version now, before continuing on. This step is important, since we have improved the modern FPI backup engine to better deal with this scenario.
  2. Identify on your target 'Local Backup' device folder, if it is either out of space now or is close to being out of space on that device, as that alone may be the reason why this issue is occuring in the first place (and jf you need to you can modify the Retention setting in the backup job(s) to decrease that value to possibly be able to help there); for help in knowing what the 'Local Backup' device folder is, you can read Steps 4-5.
  3. In the resulting backup log contents, identify and write down in a notepad file the stated warning text, for the first warning per each file that is stated in the log contents, like in the above example, the single filename (because even though 3 x files are listed in the warning, the actual filename is the same between all 3 warnings text in the backup log in that case, which won't always be true, you could have multiple filenames stated in the backup log in your case) that we are concerned with is:

    fat table not found, invalid document datafile://patch/(twfuzhkncybiewjyawqgqmfja3vw)_dev20250203151330991)sn20250426020001836 </message>

    That means that the filename itself to record for the first stated warning is this file, and at the end of the "836" part, you would need to append a ".dat" file extension to it at the end of the filename, which would equate to this complete filename in the example case:

    twfuzhkncybiewjyawqgqmfja3vw)_dev20250203151330991)sn20250426020001836.dat
  4. Use Windows Explorer to navigate to the folder that your 'Local Backup' device is assigned to, which you can see either by using the client GUI to go to the 'Device' tab, and double-click on the unmanaged 'Local Backup' device in question, that was that primary target device that the backup job had assigned to it, or if it is a managed 'Local Backup' device in question you won't be able to look at the properties of the device via the client GUI, so you will have to look at the Agent in question in the "Agent > Devices" tab via the CMon UI in that case, and there will be a "Folder or network path" (in the CMon UI that is just the "Path") variable value to read about what either local folder or network path that device was defined as.
  5. Once you are in the main folder for the 'Local Backup' device itself, you will need to drill down the folder structure a few levels to get to the actual *.dat files (which are the backup data set files that the new modern FPI backup engine utilizes, instead of *.nbd files in the old legacy backup engine). The folder with the actual *.dat files in it, will look something like 'D:\Local Drive D\data\Appl NBK\Node NBK\', for a 'Local Backup' device that utilizes a local drive folder, or '\\NAS\LocalFPI_BuffaloNAS\data\Appl NBK\Node NBK\', for a 'Local Backup' device that utilizes a network path, which will list all of the *.dat files there. This is where you will need to locate each one the single or multiple .dat files in question, that you had written down in notepad from the backup log in question, in our case that was only 1 x .dat file though if you recall, but your situation may be different, as your own backup log may have shown 4 x total .dat file names in it, to have needed to record the filenames on. While on this folder path, please confirm if the local drive or network share path is out of space or close to out of space, as stated in Step 2, before continuing to the next step, as that alone may be the reason why this issue is occuring in the first place (and jf you need to you can modify the Retention setting in the backup job(s) to decrease that value to possibly be able to help there).
  6. Still in Windows Explorer, in the folder where the actual .dat files exist, and you see them in, delete each of the exact filename(s) that were stated in the backup log in your case, which will differ from the example backup log in this KB article of course, but in that case the filename length will always be about the same, and about the same format, that contains a .dat file extension (you may need to enable "Show file extensions" in Windows Explorer to see the file extension on those files though, which is recommended to do now), otherwise you can right-click on the file in the folder, to check if it does contain a .dat file extension (that Win Explorer by default will hide or not show). Select each .dat file in that list, that matches the filenames that you had recorded in your own backup log, by right-clicking on and selecting all of those exact .dat filenames in that one folder, and then manually delete all of the exact stated filenames in that one folder. DO NOT delete all of the .dat files present in that folder, unless the folder only contains the exact same filenames, for all of the recorded filenames in your case, as in that case you could have had multiple backup jobs writing to that same single device folder, which could have been for backup jobs that are working fine and are not showing the log warnings problem for them, and you don't want to destroy that other backup job backup set .dat file data in that case (even though if you do that on accident and you do run the other backup job that is working fine, the .dat file will be re-created on that next other backup job run in the end).
  7. Once all of the exact per stated warning .dat filenames are deleted via Windows Explorer, then you can run that same backup job again, for the same backup job that had produced the warnings in it prior (which would be per backup job warnings to need to deal with manually, to delete those stated .dat files in each backup job warning, that you did deal with deleting already in Step 6), and that backup job run should be able to clean up the backups as to correct this issue.
  8. Once the next backup job run has completed, for that same backup job that had produced the backup job log warnings ("fat table not found, invalid document .." and "fct: could not locate channel in .." pair of two warnings, per .dat filename) for the stated .dat files that you had manually deleted in Step 6, then you should view the produced backup job log via the client (or CMon) Logs tab, to see if the same set of warnings show up again, or are any different, for the stated .dat filenames. Record any of the additional stated .dat files as was done in Step 3-5, if any additional warnings for .dat filenames do show up, which they shouldn't anymore but we just have to mention that here, if that possibility does become true for the next backup job run. Delete those additional stated .dat filenames in the same folder as you had done in Steps 4-5 in that case. Then run the same backup job again and see if it can complete without any of the ("fat table not found, invalid document .." and "fct: could not locate channel in .." pair of two warnings, per .dat filename) warnings in the produced backup job log.
  9. After all of that then it would be recommended to run the same backup job one more time (which will be an incremental backup job run), and confirm that no more warnings related to ("fat table not found, invalid document .." and "fct: could not locate channel in .." pair of two warnings, per .dat filename) show up. That should take care of the issue.
  10. Note: If a backup set .dat file, per FPI backup job, is ever manually deleted (or is renamed, or is for whatever reason now missing entirely as a .dat file in the folder in Step 5, that the modern FPI backup engine expects to find at the target device folder) then you may see that the next backup job run was able to backup the files or objects, but the backup job will complete with warnings status, and the produced backup log may state a single warning about ">wrn*0x0000:4001*dlt: regenerating signatures, full copies will be stored", which just means that backup job run couldn't find the .dat files to reference from so it had to produce a new "Full" backup. Then the next backup job runs after that Full backup run, should run as Incrementals after that, which should be able to complete with the Success status instead of the Warnings status after that job run that had produced the single "">wrn*0x0000:4001*dlt: regenerating signatures, full copies will be stored" warning in the backup log. And that is expected behavior for the latter.