I hope this can help anyone who is running into the same issue as us - kernels 4.1.x appear to have terrible RBD sequential write performance. Kernels before and after are great.
I tested with 4.1.6 and 4.1.15 on Ubuntu 14.04.3, ceph hammer 0.94.5 - a simple dd test yields this result:
dd if=/dev/zero of=/dev/rbd0 bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 46.3618 s, 22.6 MB/s
On 3.19 and 4.2.8, quite another story:
dd if=/dev/zero of=/dev/rbd0 bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 2.18914 s, 479 MB/s
--
Alex Gorbachev
Storcium
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