WD MyCloud EX2 Ultra 2x4TB slow write speeds over SSH

I am trying to migrate data from one WD MyCloud EX2 Ultra to another and the transfer speed using both scp and rsync is consistently around 25 MB/s.

I have ruled out networking issues (iperf shows 991 Mbits/sec) and read speed on source NAS (hdparm shows 178.73 MB/sec). The culprit is clearly target NAS write speed:

# dd if=/dev/zero of=1GB_TEST_FILE bs=1G count=1
1+0 records in
1+0 records out
1073741824 bytes (1.0GB) copied, 41.367580 seconds, 24.8MB/s

What could be the cause of this? I see the write speed is consistently low on both source and target NAS, and yet I have seen SMB transfers to source NAS reach 50-60 MB/s. What could be the reason for low write speeds when running processes from ssh shell?

EDIT: I redid my testing and found out that the write speeds were low due to large block size used by dd, when changed to 1M, write speeds are around 170 MB.

I am now looking for alternatives to rsync.


You could refer to the following links:



Thank you.

My solution is now described here:


In short: I have set up rsync server on target - this distributed CPU load for compressing/decompressing between both machines, which was a previous bottleneck.