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Is there a limit on the count of the exported devices?


independent of the size of the combined block device, I am unable to use more than 1018 devices with the "-m" option in nbd-server. So for example:

for i in {0..1999}; do truncate -s 1M mm.$i; done
sudo nbd-server -C /dev/null localhost@33333 -m /home/user/nbd/mm
sudo nbd-client localhost 33333 /dev/nbd0

Then it says:

Negotiation: ..size = 1018MB
bs=1024, sz=1067450368 bytes

which can also be confirmed by mounting /dev/nbd0.

Another example with 5000 files of 500K gives:

Negotiation: ..size = 497MB
bs=1024, sz=521216000 bytes

which gives the same 521216000/1024/500 = 1018 used files.

The same happens when using different sizes or combinations of sizes and file-counts. I am using nbd 3.20 on x64 Ubuntu 18.04. Using a configuration file makes no difference. Different hardware with the same OS and nbd version neither.

Can someone give me some pointers?


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