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Could you drop what's your SMB config in OS. (powershell - Get-SmbServerConfiguration) Mine:

On my end, if these bad apple file are inside another archive or other file this also breaks transfers. In this long ongoing topic, people report that bonding network cards may help. When I tried to tinker with network adapter settings, I only managed to bork entire config, and had to reset) Plus it's already sounds strange, why 2 network adapters would affect certain file transfer. https://forums.unraid.net/topic/79454-file-transfer-results-in-error-0x8007003b/ @JorgeB Whats your environment, Windows 11 ?

True, but would be great to figure out the reason. Because such files bork also network backups as mentioned in initial post. So you run backup, and it fails due to certain files. Had encountered same issue when made Game folder backup. Still would try to gather more evidence. Maybe more samples can help.

Unfortunately - same story.

Here are samples (https://gofile.io/d/ynZJ8m). Maybe someone else can reproduce it on their end, and see what's wrong with the files. TLDR - original files FAIL to copy. (rarely it goes through) (Store method) - repacked files FAIL if STORE compression method is used. - repacked file PASSes if DEFLATE method is used.

Heard this opinion too, tried to disable it, but same story. It's just 2 ZIP files from thousands similar. One had whitespaces in archive content filenames, but doubt it had something to do with it. With expanded SMB logs, process has these events. Those 65536 values doesn't look right, like it could be some kind of limit. May 24 13:10:14 SHAPXUB smbd[12701]: [2026/05/24 13:10:14.900685, 3] ../../source3/smbd/smb2_write.c:214(smb2_write_complete_internal) May 24 13:10:14 SHAPXUB smbd[12701]: smb2: fnum 902811720, file New Folder/2 - fail.zip, length=65536 offset=11534336 wrote=65536 May 24 13:10:14 SHAPXUB smbd[12701]: [2026/05/24 13:10:14.900927, 3] ../../source3/smbd/smb2_write.c:214(smb2_write_complete_internal) May 24 13:10:14 SHAPXUB smbd[12701]: smb2: fnum 902811720, file New Folder/2 - fail.zip, length=65536 offset=10027008 wrote=65536 May 24 13:10:14 SHAPXUB smbd[12701]: [2026/05/24 13:10:14.901193, 3] ../../source3/smbd/smb2_write.c:214(smb2_write_complete_internal) May 24 13:10:14 SHAPXUB smbd[12701]: smb2: fnum 902811720, file New Folder/2 - fail.zip, length=65536 offset=11599872 wrote=65536 May 24 13:10:14 SHAPXUB smbd[12701]: [2026/05/24 13:10:14.901430, 3] ../../source3/smbd/smb2_write.c:214(smb2_write_complete_internal) May 24 13:10:14 SHAPXUB smbd[12701]: smb2: fnum 902811720, file New Folder/2 - fail.zip, length=65536 offset=10485760 wrote=65536 May 24 13:10:14 SHAPXUB smbd[12701]: [2026/05/24 13:10:14.901713, 3] ../../source3/smbd/smb2_write.c:214(smb2_write_complete_internal) May 24 13:10:14 SHAPXUB smbd[12701]: smb2: fnum 902811720, file New Folder/2 - fail.zip, length=65536 offset=10092544 wrote=65536 May 24 13:10:14 SHAPXUB smbd[12701]: [2026/05/24 13:10:14.901926, 3] ../../source3/smbd/smb2_write.c:214(smb2_write_complete_internal) May 24 13:10:14 SHAPXUB smbd[12701]: smb2: fnum 902811720, file New Folder/2 - fail.zip, length=65536 offset=11665408 wrote=65536 May 24 13:10:14 SHAPXUB smbd[12701]: [2026/05/24 13:10:14.902185, 3] ../../source3/smbd/smb2_write.c:214(smb2_write_complete_internal) May 24 13:10:14 SHAPXUB smbd[12701]: smb2: fnum 902811720, file New Folder/2 - fail.zip, length=65536 offset=10551296 wrote=65536

Here is uncertain thing. I managed to narrow it down to particular ZIP files. (like similar was mentioned also for TrueNas - https://www.truenas.com/community/threads/copying-odd-zip-or-msi-file-causing-smb-service-to-freeze.87066/ ) (if those are repacked to 7Z it's all good and smooth) Like if such files is copied to NAS, transfer hangs a bit and becomes unresponsive. What would be proper way to pinpoint why system hangs during such file process? SMB log level, or there are other ways which may help?

Strange discovery, when backing up files with Macrium from W10 machine to Unraid, noticed that tasks fail on certain files/folders. And those even fail if I move files/rename long path to smaller one/rename end ZIPs to simple numbers. More confusion adds fact that 1000+ zips - FAILS, and 1000 is fine. Like literally those 100 are bad apples. (Okay 1000+1000 also fails) Even if I ZIP all those 1100 into single one, copying this to NAS fails as well. Zipped 1000 into one piece also goes smooth. Whaaaa. Could this be an issue because NAS runs with 4GB of RAM? While dashboard reports its barely utilized, otherwise I cannot come with anything why this strange scenarios may happens.

From few more tests, it seems Macrium Reflect doesn't handle those long file transfers straight to network disk. While VEEAM Agent handles this better. Also have seen posts where Macrium users mentioned that they do backups usually firstly disk to disk, and later move those images with more robust and reliable copy methods.

Probably will try to crank power mode to Best Performance, and see if it's better compared to Balanced. Could be also a thing when one SMB transfer is going, and some app tries to check network location, maybe in certain conditions it may have some impact.

I had SAMBA logs enabled previously, and monitored whole transfer. And those adding interface messages lead me to think, could this be interface bonding/bridging issue? I guess if interface were dropping, this would be obvious in logs.

Here are logs just after event. I start to see pattern, with 1 hour and 10 minutes. shapxub-diagnostics-20260403-1334.zip

I'm suspecting that my NIC in NAS goes down and re-appears. Like there are ton of write event, and whoops network interface appeared. New diagnostics added. After event occurred. diagnostics-20260402-2229.zip

Literally just now.

Its not like first time I have noticed, that huge file copying over network can result in errors. From what I have seen during file copy sometimes, speed goes to zero, and then it comes to software can it handle it and wait to retry, or fail. Here example case. Local Windows 10 machine file backup to network share, via MacriumReflect. Apr 2 20:12:41 SHAPXUB smbd[7525]: [2026/04/02 20:12:41.202711, 0] ../../source3/smbd/durable.c:928(vfs_default_durable_reconnect) Apr 2 20:12:41 SHAPXUB smbd[7525]: vfs_default_durable_reconnect: default_durable_reconnect_fn [GAMES--2026-04-02T18.33.49--00-00.mrbak.tmp] failed: NT_STATUS_OBJECT_NAME_NOT_FOUND durable reconnect code is shown here https://github.com/avati/samba/blob/e24fe5705e3c4d33705ebb584ea2009bb4a1a82c/source3/modules/vfs_default.c#L2429 I'm here more for advice, where to start investigation. Which kind of settings to check. And it fails in Macrium when task processes these files. https://forums.unraid.net/topic/198087-smb-drops-connections-on-long-file-transfers-and-on-certain-zip-files/#findComment-1624535 diagnostics-20260402-2054.zip