Re: Squeezing Performance of CEPH

[Alan Johnson <alanj@xxxxxxxxxxxxxx>]

We have found that we can place 18 journals on the Intel 3700 PCI-e devices comfortably, We also tried it with fio adding more jobs to ensure that performance did not drop off (via Sebastian Han’s tests described at https://www.sebastien-han.fr/blog/2014/10/10/ceph-how-to-test-if-your-ssd-is-suitable-as-a-journal-device/) so 12 should be no problem – only gotcha is if the NVMe dies . . .

 

 

From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Massimiliano Cuttini
Sent: Friday, June 23, 2017 9:35 AM
To: Ashley Merrick
Cc: ceph-users@xxxxxxxxxxxxxx
Subject: Re: [ceph-users] Squeezing Performance of CEPH

 

Hi Ashley,

You could move your Journal to another SSD this would remove the double write.

If I move the journal to another SSD, I will loss an available OSD, so this is likely to say improve of x2 and then decrease of x½ ...
this should not improve performance in any case on a full SSD disks system.

Ideally you’d want one or two PCIe NVME in the servers for the Journal.

This seems a really good Idea, but image that I have only 2 slots for PCIe and 12 SSD disks.
I image that it's will not be possible place 12 Journal on 2 PCIe NVME without loss performance..... or yes?

Or if you can hold off a bit then bluestore, which removes the double write, however is still handy to move some of the services to a seperate disk.

I hear that bluestore will remove double writing on journal (still not investigated), but I guess Luminous will be fully tested not before the end of the year.
About the today system really don't know if moving on a separate disks will have some impact considering that this is a full SSD disks system.

Even adding 2 PCIe NVME.... why should not use them as a OSD instead of journal solo?

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