i had really big performance problems with glusterfs in 2020...like 5MB/s synchronous reads and writes within a gigabit network.
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$ fio --filename=/mnt/testfile --sync=1 --rw=readwrite --bs=1024k --numjobs=1 --iodepth=1 --runtime=60 --time_based --group_reporting --name=journal-test --size=1024M
Run status group 0 (all jobs):
READ: bw=5565KiB/s (5698kB/s)
WRITE: bw=6075KiB/s (6221kB/s)