Hello Christian.
First of all, thanks for your considerations, I really appreciate it.2017-08-23 21:34 GMT-03:00 Christian Balzer <chibi@xxxxxxx>:
The only difference is:
Hello,
On Wed, 23 Aug 2017 09:11:18 -0300 Guilherme Steinmüller wrote:
> Hello!
>
> I recently installed INTEL SSD 400GB 750 SERIES PCIE 3.0 X4 in 3 of my OSD
> nodes.
>
Well, you know what's coming now, don't you?
That's a consumer device, with 70GB writes per day endurance.
unless you're essentially having a read-only cluster, you're throwing away
money.
Yes, we knew that we were going to buy a consumer device due to our limited budget and our objective of constructing a small plan of a production cloud. This model seemed acceptable. It was the top list of the consumer models on Sebastien's benchmarks
We are a lab that depends on different budget sources to accquire equipments, so they can vary and most of the time we are limited by different budget ranges.
> First of all, here's is an schema describing how my cluster is:
>
> [image: Imagem inline 1]
>
> [image: Imagem inline 2]
>
> I primarily use my ceph as a beckend for OpenStack nova, glance, swift and
> cinder. My crushmap is configured to have rulesets for SAS disks, SATA
> disks and another ruleset that resides in HPE nodes using SATA disks too.
>
> Before installing the new journal in HPE nodes, i was using one of the
> disks that today are OSDs (osd.35, osd.34 and osd.33). After upgrading the
> journal, i noticed that a dd command writing 1gb blocks in openstack nova
> instances doubled the throughput but the value expected was actually 400%
> or 500% since in the Dell nodes that we have another nova pool the
> throughput is around this value.
>
Apples, oranges and bananas.
You're comparing different HW (and no, I'm not going to look this up)
which may or may not have vastly different capabilities (like HW cache),
RAM and (unlikely relevant) CPU.
Indeed, we took this into account. The HP server were cheaper and have a poor configuration due that limited budget source.
Your NVMe may also be plugged into a different, insufficient PCIe slot for
all we know.
I checked this. I compared the slots identifying the slot information between the 3 dell nodes and 3 hp nodes by running:
The only difference is:
Dell has a parameter called
You're also using very different HDDs, which definitely will be a factor.
I thought that the backend disks would not interfer that much. For example, the ceph journal has a parameter called filestore max sync interval, which means that ceph journal will commit the transactions to the backend OSDs in a defined interval, ours is set to 35. So the client requests go first to SSD and than is commited to the OSDs.
But most importanly you're comparing 2 pools of vastly different ODS
count, no wonder a pool with 15 OSDs is faster in sequential writes than
one with 9.
> Here is a demonstration of the scenario and the difference in performance
> between Dell nodes and HPE nodes:
>
>
>
> Scenario:
>
>
> - Using pools to store instance disks for OpenStack
>
>
> - Pool nova in "ruleset SAS" placed on c4-osd201, c4-osd202 and
> c4-osd203 with 5 osds per hosts
>
SAS
>
> - Pool nova_hpedl180 in "ruleset NOVA_HPEDL180" placed on c4-osd204,
> c4-osd205, c4-osd206 with 3 osds per hosts
>
SATA
>
> - Every OSD has one partition of 35GB in a INTEL SSD 400GB 750
> SERIES PCIE 3.0 X4
>
Overkill, but since your NVMe will die shortly anyway...
With large sequential tests, the journal will have nearly NO impact on the
result, even if tuned to that effect.
>
> - Internal link for cluster and public network of 10Gbps
>
>
> - Deployment via ceph-ansible. Same configuration define in ansible
> for every host on cluster
>
>
>
> *Instance on pool nova in ruleset SAS:*
>
>
> # dd if=/dev/zero of=/mnt/bench bs=1G count=1 oflag=direct
> 1+0 records in
> 1+0 records out
> 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 2.56255 s, 419 MB/s
>
This is a very small test for what you're trying to determine and not
going to be very representative.
If for example there _is_ a HW cache of 2GB on the Dell nodes, it would
fit nicely in there.
Dell has
>
> *Instance on pool nova in ruleset NOVA_HPEDL180:*
>
> # dd if=/dev/zero of=/mnt/bench bs=1G count=1 oflag=direct
> 1+0 records in
> 1+0 records out
> 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 11.8243 s, 90.8 MB/s
>
>
> I made some FIO benchmarks as suggested by Sebastien (
> https://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to-
> test-if-your-ssd-is-suitable-as-a-journal-device/ ) and the command with 1 I'd consider a 180MB/s result from a device that supposedly does 900MB/s a
> job returned me about 180MB/s of throughput in recently installed nodes
> (HPE nodes). I made some hdparm benchmark in all SSDs and everything seems
> normal.
>
fail, but then again those tests above do NOT reflect journal usage
reality but a more of a hint if something is totally broken or not.
>
> I can't see what is causing this difference of throughput since the network
> is not a problem and i think that cpu and memory are not crucial since i
> was monitoring the cluster with atop command and i didn't notice saturation
> of resources. My only though is that I have less workload in nova_hpedl180
> pool in HPE nodes and less disks per node and this ca influence in the
> throughput of the journal.
>
How busy are your NVMe journals during that test on the Dells and HPs
respectively?
Same for the HDDs.
I can't say it now precisely, but what I can tell you for sure is that monitoring these two pools, both thoughtput and disk usage, I can see that the workload for the pool that is placed on the Dell nodes is significantly higher than the pool in the HP node. For example, the OSDs in the Dell node often keep the usage between 70% and 100%, different than HP OSDs, that vary between 10% and 40%.
Again, run longer, larger tests to get something that will actually
register, also atop with shorter intervals.
Christian
-->
> Any clue about what is missing or what is happening?
>
> Thanks in advance.
Christian Balzer Network/Systems Engineer
chibi@xxxxxxx Rakuten Communications
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