Hello,
On Wed, 29 Apr 2015 15:01:49 -0400 Anthony Levesque wrote:
We redid the test with 4MB Block Size (using the same command as before
but with 4MB for the BS) and we are getting better result from all
devices:
That's to be expected of course.
Intel DC S3500 120GB = 148 MB/s
Samsung Pro 128GB = 187 MB/s
Intel 520 120GB = 154 MB/s
Samsung EVO 1TB = 186 MB/s
Intel DC S3500 300GB = 250 MB/s
You will need to keep _both_ of these results in mind, the 4KB and 4MB
ones. For worst and best case scenarios.
And those dd tests are indicators, not a perfect replication of what Ceph
actually does.
Looking at your original results of 920MB/s over 96 1TB EVOs those SSDs
are thus capable of handling about 20MB/s combined journal/data traffic.
Ignoring any CPU limitations of course.
Unsurprisingly the best of both worlds in the SSDs you compared is the
Intel DC S3500.
And that is the slowest write and least endurable of the Intel DC SSDs.
To make a (rough) comparison between Intel and Samsung, the Intel DC S3500
are comparable to the Samsung DC Evo ones and the Intel S3700 to the
Samsung DC Pro ones.
I have not tested the DC S3610 yet but I will be ordering some soon
Those will be (for journal purposes) the worst choice when it comes to
bandwidth, as they use higher density FLASH, thus less speed at the same
size.
They are however significantly more durable than the S3500 ones at only a
slightly higher price, thus making them good candidates for a combined
journal/data SSD. IF your expected write load fits the endurance limits.
See:
http://ark.intel.com/compare/75682,86640,71914Since previously we had the journal and OSD on the same SSD Im still
wondering if having the journal separate from the SSD (with a ration of
1:3 or 1:4) will actually bring more Write speed. This is the
configuration I was thinking of if we separate the Journal from the OSD:
Your speed will go up of course.
However it will not reach the fullest potential unless you put really fast
SSDs (or a PCIe, NVMe unit like this:
http://ark.intel.com/products/79624/Intel-SSD-DC-P3700-Series-400GB-12-Height-PCIe-3_0-20nm-MLC) in there, see below.
÷Each OSD_Node÷
Dual E5-2620v2 with 64GB of RAM
Underpowered CPU when dealing with small write IOPS.
If all/most your writes are nicely coalesced by the RBD cache this may not
be a problem, but without knowing what your client VMs will do it's
impossible to predict.
-------------------
HBA 9207-8i #1
3x1TB Samsung 1TB for the Storage layer + 1 Intel S3610 200GB for the
Journal 3x1TB Samsung 1TB for the Storage layer + 1 Intel S3610 200GB
for the Journal -------------------
HBA 9207-8i #2
3x1TB Samsung 1TB for the Storage layer + 1 Intel S3610 200GB for the
Journal 3x1TB Samsung 1TB for the Storage layer + 1 Intel S3610 200GB
for the Journal -------------------
1x LSI RAID Card + 2x 120GB SSD (For OS)
2x 10GbE dual port
I suppose you already have that hardware except for the journal SSDs,
right?
I would have forgone extra OS SSDs and controllers and put the OS on the
journal SSDs in a nice RAID10.
There would be between 6-8 OSD Node like this to start the cluster.
My goal would be to max out at least 20 Gbps switch ports in writes to a
single OpenStack Compute node. (Im still not sure about the CPU capacity)
Maxing out the port can come in many flavors/ways. Most of which are not
realistic scenarios, meaning that your VMs are more likely to run out of
IOPS before they run out of bandwidth.
But to achieve something like 2GB/s writes your SSDs and/or journal SSDs
will have to handle that speed.
4x 200GB DC S3610s at 230MB/s each for journal SSDs are clearly not going
to do that.
4x 400GB DC S3700s at 460MB/s each will come pretty close to that 2GB/s,
however they will cost about the same as 2x P3700 mentioned below.
16x 800GB DC3610s as combined journal/data SSDs will give you about 4GB/s,
though.
If you want to keep using your 1TB EVOs (after having verified what their
top speed as data only SSD is, but with 16 I suppose it will be
sufficient), use 16 of them and 2 of the 400GB DC P3700 Series cards
mentioned above.
If all of the above sounds either slow or expensive you're quite right,
the old adage of "fast, good, cheap" (good being endurance here) still
holds.
And once more, having a realistic idea of how much writes will happen in
that cluster will be crucial to make the right decision here.
Having to replace your cheap SSDs after a few months when DC level SSDs
at twice the price would have lasted 5 years is something to think about.
Christian
As anyone testes a similar environment?
Anyway guys, lets me know what you think since we are still testing this
POC. ---
Anthony Lévesque
On Apr 25, 2015, at 11:46 PM, Christian Balzer <chibi@xxxxxxx> wrote:
Hello,
I think that the dd test isn't a 100% replica of what Ceph actually
does then.
My suspicion would be the 4k blocks, since when people test the maximum
bandwidth they do it with rados bench or other tools that write the
optimum sized "blocks" for Ceph, 4MB ones.
I currently have no unused DC S3700s to do a realistic comparison and
the DC S3500 I have aren't used in any Ceph environment.
When testing a 200GB DC S3700 that has specs of 35K write IOPS and
365MB/s sequential writes on mostly idle system (but on top of Ext4,
not the raw device) with a 4k dd dsync test run, atop and iostat show
a 70% SSD utilization, 30k IOPS and 70MB/s writes.
Which matches the specs perfectly.
If I do that test with 4MB blocks, the speed goes up to 330MB/s and 90%
SSD utilization according to atop, again on par with the specs.
Lastly on existing Ceph clusters with DC S3700 SSDs as journals and
rados bench and its 4MB default size that pattern continues.
Smaller sizes with rados naturally (at least on my hardware and Ceph
version, Firefly) run into the limitations of Ceph long before they hit
the SSDs (nearly 100% busy cores, journals at 4-8%, OSD HDDs anywhere
from 50-100%).
Of course using the same dd test over all brands will still give you a
good comparison of the SSDs capabilities.
But translating that into actual Ceph journal performance is another
thing.
Christian
On Sat, 25 Apr 2015 18:32:30 +0200 (CEST) Alexandre DERUMIER wrote:
I'm able to reach around 20000-25000iops with 4k block with s3500
(with o_dsync) (so yes, around 80-100MB/S).
I'l bench new s3610 soon to compare.
----- Mail original -----
De: "Anthony Levesque" <alevesque@xxxxxxxxxx>
À: "Christian Balzer" <chibi@xxxxxxx>
Cc: "ceph-users" <ceph-users@xxxxxxxxxxxxxx>
Envoyé: Vendredi 24 Avril 2015 22:00:44
Objet: Re: Possible improvements for a slow write
speed (excluding independent SSD journals)
Hi Christian,
We tested some DC S3500 300GB using dd if=randfile of=/dev/sda bs=4k
count=100000 oflag=direct,dsync
we got 96 MB/s which is far from the 315 MB/s from the website.
Can I ask you or anyone on the mailing list how you are testing the
write speed for journals?
Thanks
---
Anthony Lévesque
GloboTech Communications
Phone: 1-514-907-0050 x 208
Toll Free: 1-(888)-GTCOMM1 x 208
Phone Urgency: 1-(514) 907-0047
1-(866)-500-1555
Fax: 1-(514)-907-0750
alevesque@xxxxxxxxxx
http://www.gtcomm.net
On Apr 23, 2015, at 9:05 PM, Christian Balzer < chibi@xxxxxxx >
wrote:
Hello,
On Thu, 23 Apr 2015 18:40:38 -0400 Anthony Levesque wrote:
BQ_BEGIN
To update you on the current test in our lab:
1.We tested the Samsung OSD in Recovery mode and the speed was able
to maxout 2x 10GbE port(transferring data at 2200+ MB/s during
recovery). So for normal write operation without O_DSYNC writes
Samsung drives seem ok.
2.We then tested a couple of different model of SSD we had in stock
with the following command:
dd if=randfile of=/dev/sda bs=4k count=100000 oflag=direct,dsync
This was from a blog written by Sebastien Han and I think should be
able to show how the drives would perform in O_DSYNC writes. For
people interested in some result of what we tested here they are:
Intel DC S3500 120GB = 114 MB/s
Samsung Pro 128GB = 2.4 MB/s
WD Black 1TB (HDD) = 409 KB/s
Intel 330 120GB = 105 MB/s
Intel 520 120GB = 9.4 MB/s
Intel 335 80GB = 9.4 MB/s
Samsung EVO 1TB = 2.5 MB/s
Intel 320 120GB = 78 MB/s
OCZ Revo Drive 240GB = 60.8 MB/s
4x Samsung EVO 1TB LSI RAID0 HW + BBU = 28.4 MB/s
No real surprises here, but a nice summary nonetheless.
You _really_ want to avoid consumer SSDs for journals and have a good
idea on how much data you'll write per day and how long you expect
your SSDs to last (the TBW/$ ratio).
BQ_BEGIN
Please let us know if the command we ran was not optimal to test
O_DSYNC writes
We order larger drive from Intel DC series to see if we could get
more than 200 MB/s per SSD. We will keep you posted on tests if that
interested you guys. We dint test multiple parallel test yet (to
simulate multiple journal on one SSD).
BQ_END
You can totally trust the numbers on Intel's site:
http://ark.intel.com/products/family/83425/Data-Center-SSDs
The S3500s are by far the slowest and have the lowest endurance.
Again, depending on your expected write level the S3610 or S3700
models are going to be a better fit regarding price/performance.
Especially when you consider that loosing a journal SSD will result
in several dead OSDs.
BQ_BEGIN
3.We remove the Journal from all Samsung OSD and put 2x Intel 330
120GB on all 6 Node to test. The overall speed we were getting from
the rados bench went from 1000 MB/s(approx.) to 450 MB/s which might
only be because the intel cannot do too much in term of journaling
(was tested at around 100 MB/s). It will be interesting to test with
bigger Intel DC S3500 drives(and more journals) per node to see if I
can back up to 1000MB/s or even surpass it.
We also wanted to test if the CPU could be a huge bottle neck so we
swap the Dual E5-2620v2 from node #6 and replace them with Dual
E5-2609v2(Which are much smaller in core and speed) and the 450 MB/s
we got from he rados bench went even lower to 180 MB/s.
BQ_END
You really don't have to swap CPUs around, monitor things with atop
or other tools to see where your bottlenecks are.
BQ_BEGIN
So Im wondering if the 1000MB/s we got when the Journal was shared on
the OSD SSD was not limited by the CPUs (even though the samsung are
not good for journals on the long run) and not just by the fact
Samsung SSD are bad in O_DSYNC writes(or maybe both). It is probable
that 16 SSD OSD per node in a full SSD cluster is too much and the
major bottleneck will be from the CPU.
BQ_END
That's what I kept saying. ^.^
BQ_BEGIN
4.Im wondering if we find good SSD for the journal and keep the
samsung for normal writes and read(We can saturate 20GbE easy with
read benchmark. We will test 40GbE soon) if the cluster will keep
healthy since Samsung seem to get burnt from O_DSYNC writes.
BQ_END
They will get burned, as in have their cells worn out by any and all
writes.
BQ_BEGIN
5.In term of HBA controller, did you guys have made any test for a
full SSD cluster or even just for SSD Journal.
BQ_END
If you have separate journals and OSDs, it often makes good sense to
have them on separate controllers as well.
It all depends on density of your setup and capabilities of the
controllers.
LSI HBAs in IT mode are a known and working entity.
Christian
--
Christian Balzer Network/Systems Engineer
chibi@xxxxxxx Global OnLine Japan/Fusion Communications
http://www.gol.com/
--
Christian Balzer Network/Systems Engineer
chibi@xxxxxxx
Global OnLine Japan/Fusion Communications
http://www.gol.com/
