[gpfsug-discuss] Anybody running GPFS over iSCSI? -

[Sanchez, Paul]

Using iSCSI with Spectrum Scale is definitely do-able.  As with running Scale in general, your networking needs to be very solid.  For iSCSI the best practice I’m aware of is the dedicated/simple approach described by JF below: one subnet per switch (failure domain), nothing fancy like VRRP/HSRP/STP, and let multipathd do its job at ensuring that the available paths are the ones being used.

We have also had some good experiences using routed iSCSI (which fits the rackscale/hyperscale style deployment model too, but this implies that you have a good QoS plan to assure that markings are correct and any link which can become congested can’t completely starve the dedicated queue you should be using for iSCSI.  It’s also a good practice for the other TCP traffic in your non-iSCSI queue to use ECN in order to keep switch buffer utilization low.  (As of today, I haven’t seen any iSCSI arrays which support ECN.)  If you’re sharing arrays with multiple clusters/filesystems (i.e. not a single workload), then I would also recommend using iSCSI arrays which support per-volume/volume-group QOS limits to avoid noisy-neighbor problems in the iSCSI realm.  As of today, there are even 100GbE capable all-flash solutions available which work well with Scale.

Lastly, I’d say that iSCSI might not be the future… but NVMeOF hasn’t exactly given us many products ready to be the present.  Most of the early offerings in this space are under-featured, over-priced, inflexible, proprietary, or fragile.  We are successfully using non-standards based NVMe solutions today with Scale, but they have much more stringent and sensitive networking requirements (e.g. non-routed dedicated networking with PFC for RoCE) in order to provide reliable performance.  So far, we’ve found these early offerings best-suited for single-workload use cases.  I do expect this to continue to develop and improve on price, features, reliability/fragility.

Thx
Paul

From: gpfsug-discuss-bounces at spectrumscale.org <gpfsug-discuss-bounces at spectrumscale.org> On Behalf Of Jan-Frode Myklebust
Sent: Sunday, December 16, 2018 8:46 AM
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Subject: Re: [gpfsug-discuss] Anybody running GPFS over iSCSI? -


I have been running GPFS over iSCSI, and know of customers who are also. Probably not in the most demanding environments, but from my experience iSCSI works perfectly fine as long as you have a stable network. Having a dedicated (simple) storage network for iSCSI is probably a good idea (just like for FC), otherwise iSCSI or GPFS is going to look bad when your network admins cause problems on the shared network.


-jf
søn. 16. des. 2018 kl. 12:59 skrev Frank Kraemer <kraemerf at de.ibm.com<mailto:kraemerf at de.ibm.com>>:

Kevin,

Ethernet networking of today is changing very fast as the driving forces are the "Hyperscale" datacenters. This big innovation is changing the world and is happening right now. You must understand the conversation by breaking down the differences between ASICs, FPGAs, and NPUs in modern Ethernet networking.

1) Mellanox has a very good answer here based on the Spectrum-2 chip
http://www.mellanox.com/page/press_release_item?id=1933

2) Broadcom's answer to this is the 12.8 Tb/s StrataXGS Tomahawk 3 Ethernet Switch Series
https://www.broadcom.com/products/ethernet-connectivity/switching/strataxgs/bcm56980-series
https://globenewswire.com/news-release/2018/10/24/1626188/0/en/Broadcom-Achieves-Mass-Production-on-Industry-Leading-12-8-Tbps-Tomahawk-3-Ethernet-Switch-Family.html

3) Barefoots Tofinio2 is another valid answer to this problem as it's programmable with the P4 language (important for Hyperscale Datacenters)
https://www.barefootnetworks.com/

The P4 language itself is open source. There’s details at p4.org<http://p4.org>, or you can download code at GitHub: https://github.com/p4lang/

4) The last newcomer to this party comes from Innovium named Teralynx
https://innovium.com/products/teralynx/
https://innovium.com/2018/03/20/innovium-releases-industrys-most-advanced-switch-software-platform-for-high-performance-data-center-networking-2-2-2-2-2-2/

(Most of the new Cisco switches are powered by the Teralynx silicon, as Cisco seems to be late to this game with it's own development.)

So back your question - iSCSI is not the future! NVMe and it's variants is the way to go and these new ethernet swichting products does have this in focus.
Due to the performance demands of NVMe, high performance and low latency networking is required and Ethernet based RDMA — RoCE, RoCEv2 or iWARP are the leading choices.

-frank-

P.S. My Xmas wishlist to the IBM Spectrum Scale development team would be a "2019 HighSpeed Ethernet Networking optimization for Spectrum Scale" to make use of all these new things and options :-)

Frank Kraemer
IBM Consulting IT Specialist / Client Technical Architect
Am Weiher 24, 65451 Kelsterbach, Germany
mailto:kraemerf at de.ibm.com
Mobile +49171-3043699
IBM Germany
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