topic Re: Why does "fio write" change the performance of "fio read" in Solid State Drives (NAND)

Why does "fio write" change the performance of "fio read"

YLin34 — Fri, 20 Apr 2018 18:17:44 GMT

I have a P4600 2TB NVMe SSD. Right after I used Intel SSD toolbox to secure erase it, fio reports 4kB random read at 809K IOPS.

sudo fio --name=dummy --size=10G --filename=/dev/nvme0n1 --ioengine=libaio --direct=1 --rw=randread -bs=4k** --iodepth=64 --numjobs=4 --group_reporting

However, after I tried to pre-conditioning the SSD with the following write command

sudo fio --name=dummy --size=2000G --filename=/dev/nvme0n1 --ioengine=libaio --direct=1 --rw=write -bs=4k** --iodepth=64 --numjobs=1 --group_reporting (I also tried --size=1700G, the result is the same)

the randread command above is now reporting 4kB at 520k IOPS.

So why such a severe drop?

Re: Why does "fio write" change the performance of "fio read"

idata — Fri, 20 Apr 2018 22:34:48 GMT

Hi yaolin,

Thank you for contacting our support community. We understand your situation regarding the Intel® SSD DC P4600 Series. We recommend you to check the following https://itpeernetwork.intel.com/how-to-benchmark-ssds-with-fio-visualizer/ article related to how to benchmark SSDs with FIO*. You will be able to find the settings for the test. Regarding the number, we recommend you to check the https://ark.intel.com/products/96999/Intel-SSD-DC-P4600-Series-2_0TB-12-Height-PCIe-3_1-x4-3D1-TLC performance information related to the SSD. As per the website, the SSD has the following stats: Performance :Sequential Read (up to) 3200 MB/sSequential Write (up to) 1575 MB/sRandom Read (100% Span) 610000 IOPSRandom Write (100% Span) 196650 IOPSIf you get the 75% of the numbers or better, it means that the SSD is working fine. As an example: Random Read: 610000 IOPS75% of 610000 = 457500 IOPS and you are getting 809K which is above of the advertised speed. Keep in mind that SSD was empty before the test. For the Random Write: 196650 IOPS75% of 196650 = 147487.5 IOPS.Based on the information, after pre-conditioning the SSD you got 520k IOPS which represents the 85.6% of the random reads based on the drive specs. Keep in mind that at this point there is information written in the SSD so the numbers may vary. Regards, Junior M.

Re: Why does "fio write" change the performance of "fio read"

YLin34 — Sat, 21 Apr 2018 00:17:45 GMT

Hi,

Thanks for the quick response and the great links.

No, I was not complaining about the performance itself. I was just trying to understand why the IOPS drops.

I was thinking that, right after secure erase the SSD, FTL table is also erased. This table will need to be build and thus the first randread could be slower. Yet I got 809k IOPS.

Then I sequentially wrote through most of the drive once (1.7TB out of 2.0TB). Since I wrote only once, there shall be no erase involved and thus there shall be no garbage collection.

But then, why did the IOPS drop to 520k when I did randread again? You mentioned this is a normal IOPS. Then maybe I shall ask why IOPS is so high in the first randread. I don't know why SSD is empty vs has data would impact the read throughput.

Thanks,

Yao

Re: Why does "fio write" change the performance of "fio read"

idata — Mon, 23 Apr 2018 15:50:36 GMT

Hi yaolin,

Thanks for the reply. In order to answer your question regarding why the SSD performance slows down as it becomes full, we recommend you to check the following articles: https://www.howtogeek.com/165542/why-solid-state-drives-slow-down-as-you-fill-them-up/ Why Solid-State Drives Slow Down As You Fill Them Up https://pureinfotech.com/why-solid-state-drive-ssd-performance-slows-down/ Why solid-state drive (SSD) performance slows down as it becomes full If you have further questions then feel free to contact us again. NOTE: Any links provided for third party tools or sites are offered for your convenience and should not be viewed as an endorsement by Intel® of the content, products, or services offered there. We do not offer support for any third party tool mentioned here.Regards, Junior M.

Re: Why does "fio write" change the performance of "fio read"

YLin34 — Mon, 23 Apr 2018 16:34:03 GMT

I understand that the write perform will drop as the SSD fills up. But I am doing random read only in this case.

Re: Why does "fio write" change the performance of "fio read"

idata — Mon, 23 Apr 2018 23:25:22 GMT

Hi yaolin,

We would like to let you know that this process can affect the sequential and random reads as well. Also, several factors can affect the score:

Processor Performance
Platform Performance
I/O and Peripheral Performance

You can check the following http://manuals.ts.fujitsu.com/file/12176/fujitsu_intel-ssd-dc-pcie-eg-en.pdf evaluation guide for the Intel® SSD DC P3700 Series, this does not apply to your SSD but the terminology is the same.

Regards,

Junior M.

Re: Why does "fio write" change the performance of "fio read"

idata — Mon, 30 Apr 2018 18:04:29 GMT

Hi yaolin,

We would like to know if you read our previous post. If you have any other questions, we'll be waiting for your response.Regards, Junior M.