Date: Sun, 19 Jun 2016 21:54:22 -0400 (EDT) From: Rick Macklem <rmacklem@uoguelph.ca> To: Jordan Hubbard <jkh@ixsystems.com> Cc: freebsd-fs <freebsd-fs@freebsd.org>, Alexander Motin <mav@freebsd.org> Subject: Re: pNFS server Plan B Message-ID: <1996808572.159331289.1466387661988.JavaMail.zimbra@uoguelph.ca> In-Reply-To: <D20C793E-A2FD-49F3-AD88-7C2FED5E7715@ixsystems.com> References: <1524639039.147096032.1465856925174.JavaMail.zimbra@uoguelph.ca> <D20C793E-A2FD-49F3-AD88-7C2FED5E7715@ixsystems.com>
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Jordan Hubbard wrote: >=20 > > On Jun 13, 2016, at 3:28 PM, Rick Macklem <rmacklem@uoguelph.ca> wrote: > >=20 > > You may have already heard of Plan A, which sort of worked > > and you could test by following the instructions here: > >=20 > > http://people.freebsd.org/~rmacklem/pnfs-setup.txt > >=20 > > However, it is very slow for metadata operations (everything other than > > read/write) and I don't think it is very useful. >=20 > Hi guys, >=20 > I finally got a chance to catch up and bring up Rick=E2=80=99s pNFS setup= on a couple > of test machines. He=E2=80=99s right, obviously - The =E2=80=9Cplan A=E2= =80=9D approach is a bit > convoluted and not at all surprisingly slow. With all of those transits > twixt kernel and userland, not to mention glusterfs itself which has not > really been tuned for our platform (there are a number of papers on this = we > probably haven=E2=80=99t even all read yet), we=E2=80=99re obviously stil= l in the =E2=80=9Cfirst > make it work=E2=80=9D stage. >=20 > That said, I think there are probably more possible plans than just A and= B > here, and we should give the broader topic of =E2=80=9Cwhat does FreeBSD = want to do > in the Enterprise / Cloud computing space?" at least some consideration a= t > the same time, since there are more than a few goals running in parallel > here. >=20 > First, let=E2=80=99s talk about our story around clustered filesystems + = associated > command-and-control APIs in FreeBSD. There is something of an embarrassm= ent > of riches in the industry at the moment - glusterfs, ceph, Hadoop HDFS, > RiakCS, moose, etc. All or most of them offer different pros and cons, a= nd > all offer more than just the ability to store files and scale =E2=80=9Cel= astically=E2=80=9D. > They also have ReST APIs for configuring and monitoring the health of the > cluster, some offer object as well as file storage, and Riak offers a > distributed KVS for storing information *about* file objects in addition = to > the object themselves (and when your application involves storing and > managing several million photos, for example, the idea of distributing th= e > index as well as the files in a fault-tolerant fashion is also compelling= ). > Some, if not most, of them are also far better supported under Linux than > FreeBSD (I don=E2=80=99t think we even have a working ceph port yet). I= =E2=80=99m not > saying we need to blindly follow the herds and do all the same things oth= ers > are doing here, either, I=E2=80=99m just saying that it=E2=80=99s a much = bigger problem > space than simply =E2=80=9Cparallelizing NFS=E2=80=9D and if we can kill = multiple birds with > one stone on the way to doing that, we should certainly consider doing so= . >=20 > Why? Because pNFS was first introduced as a draft RFC (RFC5661 > <https://datatracker.ietf.org/doc/rfc5661/>) in 2005. The linux folks ha= ve > been working on it > <http://events.linuxfoundation.org/sites/events/files/slides/pnfs.pdf>; si= nce > 2006. Ten years is a long time in this business, and when I raised the > topic of pNFS at the recent SNIA DSI conference (where storage developers > gather to talk about trends and things), the most prevalent reaction I go= t > was =E2=80=9Cpeople are still using pNFS?!=E2=80=9D This is clearly one= of those > technologies that may still have some runway left, but it=E2=80=99s been = rapidly > overtaken by other approaches to solving more or less the same problems i= n > coherent, distributed filesystem access and if we want to get mindshare f= or > this, we should at least have an answer ready for the =E2=80=9Cwhy did yo= u guys do > pNFS that way rather than just shimming it on top of ${someNewerHotness}?= ?=E2=80=9D > argument. I=E2=80=99m not suggesting pNFS is dead - hell, even AFS > <https://www.openafs.org/>; still appears to be somewhat alive, but there= =E2=80=99s a > difference between appealing to an increasingly narrow niche and trying t= o > solve the sorts of problems most DevOps folks working At Scale these days > are running into. >=20 Here are a few pNFS papers from the Netapp and Panansas sites. They are dated 2012->2015: (these papers give a nice overview of what pNFS is) http://www.netapp.com/us/media/tr-4063.pdf http://www.netapp.com/us/media/tr-4239.pdf http://www.netapp.com/us/media/wp-7153.pdf http://www.panasas.com/products/pnfs-overview One of these notes that the first Linux distribution that shipped with pNFS support was RHEL6.4 in 2013. So, I have no idea if it will catch on, but I don't think it can be conside= red end of life. (Many use NFSv3 and its RFC is dated June 1995.) rick > That is also why I am not sure I would totally embrace the idea of a cent= ral > MDS being a Real Option. Sure, the risks can be mitigated (as you say, b= y > mirroring it), but even saying the words =E2=80=9Ccentral MDS=E2=80=9D (o= r central anything) > may be such a turn-off to those very same DevOps folks, folks who have be= en > burned so many times by SPOFs and scaling bottlenecks in large environmen= ts, > that we'll lose the audience the minute they hear the trigger phrase. Ev= en > if it means signing up for Other Problems later, it=E2=80=99s a lot easie= r to =E2=80=9Csell=E2=80=9D > the concept of completely distributed mechanisms where, if there is any > notion of centralization at all, it=E2=80=99s at least the result of a qu= orum > election and the DevOps folks don=E2=80=99t have to do anything manually = to cause it > to happen - the cluster is =E2=80=9Cresilient" and "self-healing" and the= y are happy > with being able to say those buzzwords to the CIO, who nods knowingly and > tells them they=E2=80=99re doing a fine job! >=20 > Let=E2=80=99s get back, however, to the notion of downing multiple avians= with the > same semi-spherical kinetic projectile: What seems to be The Rage at the > moment, and I don=E2=80=99t know how well it actually scales since I=E2= =80=99ve yet to be at > the pointy end of such a real-world deployment, is the idea of clustering > the storage (=E2=80=9Csomehow=E2=80=9D) underneath and then providing NFS= and SMB protocol > access entirely in userland, usually with both of those services cooperat= ing > with the same lock manager and even the same ACL translation layer. Our > buddies at Red Hat do this with glusterfs at the bottom and NFS Ganesha + > Samba on top - I talked to one of the Samba core team guys at SNIA and he > indicated that this was increasingly common, with the team having helped > here and there when approached by different vendors with the same idea. = We > (iXsystems) also get a lot of requests to be able to make the same file(s= ) > available via both NFS and SMB at the same time and they don=E2=80=99t mu= ch at all > like being told =E2=80=9Cbut that=E2=80=99s dangerous - don=E2=80=99t do = that! Your file contents > and permissions models are not guaranteed to survive such an experience!= =E2=80=9D > They really want to do it, because the rest of the world lives in > Heterogenous environments and that=E2=80=99s just the way it is. >=20 > Even the object storage folks, like Openstack=E2=80=99s Swift project, ar= e spending > significant amounts of mental energy on the topic of how to re-export the= ir > object stores as shared filesystems over NFS and SMB, the single consiste= nt > and distributed object store being, of course, Their Thing. They wish, o= f > course, that the rest of the world would just fall into line and use thei= r > object system for everything, but they also get that the "legacy stuff=E2= =80=9D just > won=E2=80=99t go away and needs some sort of attention if they=E2=80=99re= to remain players > at the standards table. >=20 > So anyway, that=E2=80=99s the view I have from the perspective of someone= who > actually sells storage solutions for a living, and while I could certainl= y > =E2=80=9Csell some pNFS=E2=80=9D to various customers who just want to ad= d a dash of > steroids to their current NFS infrastructure, or need to use NFS but also > need to store far more data into a single namespace than any one box will > accommodate, I also know that offering even more elastic solutions will b= e a > necessary part of offering solutions to the growing contingent of folks w= ho > are not tied to any existing storage infrastructure and have various > non-greybearded folks shouting in their ears about object this and cloud > that. Might there not be some compromise solution which allows us to put > more of this in userland with less context switches in and out of the > kernel, also giving us the option of presenting a more united front to > multiple protocols that require more ACL and lock impedance-matching than > we=E2=80=99d ever want to put in the kernel anyway? >=20 > - Jordan >=20 >=20 >=20 >=20
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