Re: NVRAM cards as OSD journals

[Heath Albritton <halbritt@xxxxxxxx>]

I'm contemplating the same thing as well.  Or rather, I'm actually doing some testing.  I have a Netlist EV3 and have seen ~6GB/s read and write for any block size larger than 16k or so, IIRC.

Sebastien Han has a blog page with journal benchmarks, I've added the specifics there.

This week, I expect to test the performance with ceph on a single node.  I have two identically configured nodes, each with 8 SATA SSDs as OSDs.  My goal is to see if the nvram card improves the performance, specifically with regard to latency.

The Netlist folks claim significantly improved performance for 64k blocks with ceph.  Thy and reduced latency bodes well for database type use cases.

-H

On May 20, 2016, at 08:52, EP Komarla <Ep.Komarla@xxxxxxxxxxxxxxx> wrote:

Hi,

 

I am contemplating using a NVRAM card for OSD journals in place of SSD drives in our ceph cluster.   

 

Configuration:

·         4 Ceph servers

·         Each server has 24 OSDs (each OSD is a 1TB SAS drive)

·         1 PCIe NVRAM card of 16GB capacity per ceph server

·         Both Client & cluster network is 10Gbps

 

As per ceph documents:

The expected throughput number should include the expected disk throughput (i.e., sustained data transfer rate), and network throughput. For example, a 7200 RPM disk will likely have approximately 100 MB/s. Taking the min() of the disk and network throughput should provide a reasonable expected throughput. Some users just start off with a 10GB journal size. For example:

osd journal size = 10000

Given that I have a single 16GB card per server that has to be carved among all 24OSDs, I will have to configure each OSD journal to be much smaller around 600MB, i.e., 16GB/24 drives.  This value is much smaller than 10GB/OSD journal that is generally used.  So, I am wondering if this configuration and journal size is valid.  Is there a performance benefit of having a journal that is this small?  Also, do I have to reduce the default “filestore maxsync interval” from 5 seconds to a smaller value say 2 seconds to match the smaller journal size?

 

Have people used NVRAM cards in the Ceph clusters as journals?  What is their experience?

 

Any thoughts?

 

 

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