[Gluster-users] Gluster linear scale-out performance

[Qing Wang]

Hi,

I am trying to test Gluster linear scale-out performance by adding more
storage server/bricks, and measure the storage I/O performance. To vary the
storage server number, I create several "stripe" volumes that contain 2
brick servers, 3 brick servers, 4 brick servers, and so on. On gluster
client side, I used "dd if=/dev/zero of=/mnt/glusterfs/dns_test_data_26g
bs=1M count=26000" to create 26G data (or larger size), and those data will
be distributed to the corresponding gluster servers (each has gluster brick
on it) and "dd" returns the final I/O throughput. The Internet is 40G
infiniband, although I didn't do any specific configurations to use
advanced features.

What confuses me is that the storage I/O seems not to relate to the number
of storage nodes, but Gluster documents said it should be linear scaling.
For example, when "write-behind" is on, and when Infiniband "jumbo frame"
(connected mode) is on, I can get ~800 MB/sec reported by "dd", no matter I
have 2 brick servers or 8 brick servers -- for 2 server case, each server
can have ~400 MB/sec; for 4 server case, each server can have ~200MB/sec.
That said, each server I/O does aggregate to the final storage I/O (800
MB/sec), but this is not "linear scale-out".

Can somebody help me to understand why this is the case? I certainly can
have some misunderstanding/misconfiguration here. Please correct me if I
do, thanks!

Best,
Qing
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