Finally understood the reason why Samba 4.7.4 wastes huge RAM on NAS4Free 11.1.0.4 [のふ処|NOFUDOKORO]

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====== Finally understood the reason why Samba 4.7.4 wastes huge RAM on NAS4Free 11.1.0.4 ======

I experienced the Samba daemons wolfed a lot of memories when I looked into bad behaviour of CIFS shareing on my friend's NAS. They wastesd gigabyte order memories per one process, then consumed 16GB of physical memory and 64GB of swap. I had no choice but to shut down the machine forcibly. It was clearly unusual. I think the lack of memory caused proximately the problem because ARC couldn't use enough memory and therefore storage performance was poor.

I tried to fiddle with some options, then it seemed a shadow copy option brought the disaster. A following picture shows difference between the option 'On' and 'Off' of ''top'' command.

<WRAP centeralign>
{{ :blog:2018:samba_memory_usage_comparison_whether_shadow_copy_enabled.png |}}
Left-side is "Shadow copy enabled", right-side is "disabled."
</WRAP>


It is alarmingly at-a-glance. The memory usages were different order of magnitude literally. The samba enabled shadow copy option almost dried up the memory in less than a day, on the other hand, disabled one works fine four-day-old alghough the load average is up to 13. FYI, the file sharing service also works in this situation.

The VSS in Samba means a ''vfs_shadow_copy2'' module has some bugs, doesn't it? I felt there were no problem if the options was enabled when NAS4Free was version 9 or 10 although my memory was so dim.