[Gluster-users] Gluster linear scale-out performance

Yaniv Kaul ykaul at redhat.com
Tue Jul 21 18:53:29 UTC 2020

On Tue, 21 Jul 2020, 21:43 Qing Wang <qw at g.clemson.edu> wrote:

> Hi Yaniv,
> Thanks for the quick response. I forget to mention I am testing the
> writing performance, not reading. In this case, would the client cache hit
> rate still be a big issue?

It's not hitting the storage directly. Since it's also single threaded, it
may also not saturate it. I highly recommend testing properly.

> I'll use fio to run my test once again, thanks for the suggestion.
> Thanks,
> Qing
> On Tue, Jul 21, 2020 at 2:38 PM Yaniv Kaul <ykaul at redhat.com> wrote:
>> On Tue, 21 Jul 2020, 21:30 Qing Wang <qw at g.clemson.edu> wrote:
>>> 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.
>> Your dd command is inaccurate, as it'll hit the client cache. It is also
>> single threaded. I suggest switching to fio.
>> Y.
>>> 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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