Alright, so I've done a bit further research, looks like the DIMM on NVMe did 
not go to public market except found in some NetAPP storage appliace.

However, this product has been evolved to use the memory slot on the 
motherboard directly and becomes a NVDIMM project. HPE is said to launch those 
servers last year, don't know if it is on the market yet.

http://searchsolidstatestorage.techtarget.com/news/450280262/HPE-launches-NVDIMM-NVMe-persistent-memory-products

Regards,
Horace Ng
-
ISL HK Limited
E-mail: hor...@hkisl.net
Tel: +852 27109880
Fax: +852 27704631

----- Original Message -----
From: "Christian Balzer" <ch...@gol.com>
To: "ceph-users" <ceph-us...@ceph.com>
Cc: "horace" <hor...@hkisl.net>
Sent: Wednesday, February 22, 2017 3:37:18 PM
Subject: Re: [ceph-users] NVRAM cache for ceph journal

Hello,

On Wed, 22 Feb 2017 15:07:48 +0800 (HKT) Horace wrote:

> Dear all,
> 
> Is anybody got any experience on this product? It is a BBU backed NVRAM 
> cache, I think it is most fit on Ceph.
> 
> https://www.microsemi.com/products/storage/flashtec-nvram-drives/nv1616
> 
Not this product, but some people here on this ML looked at similar things
in the past.

And while fast and won't wear out, it's hard to find a good
(economical) use case for these.

1. For HDD backed OSDs this kind of NVRAM unit is overkill and at 16GB
also something that may prove too small with more than 8 HDDs. 

2. For SSD backed OSDs it's a much better fit, however can you afford both
and more importantly do you need that performance and can actually realize
it? Your CPUs are going to become bottlenecks at some point.

3. For NVMe backed OSDs it would be a good fit, too. But given the PCIe
lanes needed you may wind up only with 4 OSDs per node. Also the fastest
CPUs you can find (high speed, not cores). And the price tag of this combo
is going to be something for specialist use and/or really well funded
operations. 

Lastly while BlueStore will of course also profit from some of its data on
fast storage (WAL, DB) the exact size requirements are not exactly clear
to me at this time. 
What it definitely won't need are (relatively large) journals.

Christian
-- 
Christian Balzer        Network/Systems Engineer                
ch...@gol.com           Global OnLine Japan/Rakuten Communications
http://www.gol.com/

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