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@xxxxxxxxxx> wrote:
On Tue, 21 Jul 2020, 21:43 Qing Wang <qw@xxxxxxxxxxxxx> 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,QingOn Tue, Jul 21, 2020 at 2:38 PM Yaniv Kaul <ykaul@xxxxxxxxxx> wrote:On Tue, 21 Jul 2020, 21:30 Qing Wang <qw@xxxxxxxxxxxxx> 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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