[Gluster-users] Gluster linear scale-out performance

[Qing Wang]

fio gives me the correct linear scale-out results, and you're right, the
storage cache is the root cause that makes the dd measurement results not
accurate at all.

Thanks,
Qing


On Tue, Jul 21, 2020 at 2:53 PM Yaniv Kaul <ykaul at redhat.com> wrote:

>
>
> 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.
> Y.
>
>
>> 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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