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 Post subject: NVME Disks
PostPosted: Fri May 29, 2020 3:38 am 

Joined: Wed Jun 13, 2018 2:31 am
Posts: 13
Hi,

Anyone here has primera and is using NVME SCM

from the primera datasheet i can't seem to find any SKU for NVME

is primera design to use NVME SCM as a cache for the SAS Flash drives ?

any additional thoughts for lacking of full fledged NVME for the array ?


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 Post subject: Re: NVME Disks
PostPosted: Fri May 29, 2020 6:52 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1104
Location: Europe
No NVMe or SCM available for Primera today but the system is NVMe ready.

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 Post subject: Re: NVME Disks
PostPosted: Thu Jun 11, 2020 3:20 am 

Joined: Sun Oct 12, 2014 2:02 pm
Posts: 22
Location: Örebro Sweden
In the latest QuicSpec from june 10 you can find new nvme disks and 10/25 host bus adapters

https://h20195.www2.hpe.com/v2/getdocument.aspx?docname=a00067738enw


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 Post subject: Re: NVME Disks
PostPosted: Thu Jun 18, 2020 4:44 am 

Joined: Wed Jun 13, 2018 2:31 am
Posts: 13
so with 16 NVME slots in the A650/A670 chassis

and the rest is SAS, any reason to have a split on the cpg between NVME or SAS ?

i dont see any documentation stating the usage of the nvme and the sas

and in what scenario i should use SAS SSD vs NVME SSD


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 Post subject: Re: NVME Disks
PostPosted: Thu Jun 18, 2020 6:37 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1104
Location: Europe
My guess (and this is only a guess) is not to seperate. On a 2-node system you will get 8 NVMe drives. Even if NVMe is a better protocol, I doubt that the possible negative effect of SCSI-based protocal is more than the possitive effect of having more drives to share the load.

Where NVMe will shine is the reduced latency over SCSI protocol... but the "affordable" flash medias today still carry a significant amount of latency. Based on the list price of SAS and NVMe drives in Primera I'm pretty sure it's about the same or exactly the same flash media used in both type of drives.

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 Post subject: Re: NVME Disks
PostPosted: Thu Jun 18, 2020 8:12 pm 

Joined: Wed Jun 13, 2018 2:31 am
Posts: 13
if the recommendation is to put SAS+NVME disks in the same CPG, won't there be a inconsistent
performance/latency skew due to the different interface ?

notice there is no NVME SCM also, so we can't do like AFC of NVME SCM with SAS SSD right

im very surprise that primera isn't a full NVME capable on the base/controller chassis


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 Post subject: Re: NVME Disks
PostPosted: Fri Jun 19, 2020 12:10 pm 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1104
Location: Europe
JinSXS wrote:
if the recommendation is to put SAS+NVME disks in the same CPG, won't there be a inconsistent
performance/latency skew due to the different interface ?

notice there is no NVME SCM also, so we can't do like AFC of NVME SCM with SAS SSD right

im very surprise that primera isn't a full NVME capable on the base/controller chassis


As mentioned in previous post, I don't think there is a different in throughput/iops performance between the drives. As for latency you get the latency of the slowest drives.. so NVMe only CPG probably may provide lower throughput and lower latency. I think most people will take 100% higher throughput vs 5-10% lower latency (already well below 1msec). Remember that best practice is "what works best for most", not the answer to everything.

Remember that AFC was read only. You can get a Primera 670 with 1TB cache per node which will also do write. Sounds like a better option :).

Full NVMe in base chassis is probably a simple math question. Each NVMe slot uses 4 PCIe lanes. 4x24 = 96 PCIe lanes. Not sure what CPU and PCIe lanes available is in the Primera, but I'm guessing that after dedicating PCIe lanes to ASICs, HBAs (FC/iSCSI/SAS), RCIP ports etc that there is nowhere near 96 left..... my guess is that if they made a solution for 24 NVMe slots in node chassis, they also solved how to get NVMe to expansion cages which they haven't yet.

But I'm guessing this is the evolution. First get NVMe as a proven technology in production systems. Then make it scale before SCM (or similar) flash technology becomes mainstream and the real difference between NVMe and SAS is visible.

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