I have 6 x Samsung SSD 840 pro drives in an RAID 0 configuration (mdraid).

When I write to a non-DRBD partition on the drive, bypassing caches, I get 400 
MB/sec.

When I trim a filesystem mounted on a non-DRBD partition, it finishes fast.

When I write to a DRBD replicated volume, I get 80MB/sec, which is about when I 
would expect using protocol C over a gigabit network.

When I trim a filesystem that is mounted on a drbd device it is extremely slow. 
It takes three days to trim a 1.2TB volume.

Running iperf between nodes shows 900Mbits/sec bandwidth, <1 ms latency, no 
packet loss.

Why is trimming a DRBD volume so slow? This makes the servers unusable.

--
Eric Robinson

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