[ceph-users] data loss on full file system?

Hi, for test purposes, I have set up two 100 GB OSDs, one taking a data pool and the other metadata pool for cephfs. Am running 14.2.6-1-gffd69200ad-1 with packages from https://mirror.croit.io/debian-nautilus Am then running a program that creates a lot of 1 MiB files by calling fopen() fwrite() fclose() for each of them. Error codes are checked. This works successfully for ~100 GB of data, and then strangely also succeeds for many more 100 GB of data... ?? All written files have size 1 MiB with 'ls', and thus should contain the data written. However, on inspection, the files written after the first ~100 GiB, are full of just 0s. (hexdump -C) To further test this, I use the standard tool 'cp' to copy a few random-content files into the full cephfs filessystem. cp reports no complaints, and after the copy operations, content is seen with hexdump -C. However, after forcing the data out of cache on the client by reading other earlier created files, hexdump -C show all-0 content for the files copied with 'cp'. Data that was there is suddenly gone...? I am new to ceph. Is there an option I have missed to avoid this behaviour? (I could not find one in https://docs.ceph.com/docs/master/man/8/mount.ceph/ ) Is this behaviour related to https://docs.ceph.com/docs/mimic/cephfs/full/ ? (That page states 'sometime after a write call has already returned 0'. But if write returns 0, then no data has been written, so the user program would not assume any kind of success.) Best regards, Håkan