topic Re: Why Does Using a UNC Path Toss a Warning? in ArcGIS Enterprise Questions

Why Does Using a UNC Path Toss a Warning?

JoeBorgione — Tue, 28 Jun 2016 14:52:50 GMT

10.3.1 ArcGIS Server.

When I analyze a map service prior to publishing it, the analysis tosses a warning about using UNC paths. Why is that? Is there a more appropriate way to map to data stored on a network san?

Re: Why Does Using a UNC Path Toss a Warning?

DanPatterson_Retired — Tue, 28 Jun 2016 15:02:39 GMT

Under your Co... field is it a code like this one?

10027: Layer's data source is referenced via a UNC path—Help | ArcGIS for Desktop

Backgrounder for others Paths explained: Absolute, relative, UNC, and URL—Help | ArcGIS for Desktop

Re: Why Does Using a UNC Path Toss a Warning?

MichaelMiller2 — Tue, 28 Jun 2016 15:09:46 GMT

It's basically telling you that there may be reduced performance when using UNC data connections as opposed to direct connections. If you are sharing data on a network, really no way around it. Besides, the reduction in performance is very small if any, depending on your network.

Re: Why Does Using a UNC Path Toss a Warning?

JoeBorgione — Tue, 28 Jun 2016 16:25:57 GMT

Thanks guys- as far as performance goes, I can't imagine it being much of a hit for a couple reasons: The Map Service is only being read internally, and it's only being read by a third party application (9-1-1 dispatch CAD) to get data like dispatch zones and city of a given address point. So, no drawing involved per se.

Yes Dan, when I expand the COde field it is 10027.

edit: So I guess I'll just shine the warning.

Dan Patterson

Michael Miller

Re: Why Does Using a UNC Path Toss a Warning?

JoshuaBixby — Tue, 28 Jun 2016 17:28:35 GMT

Accessing any data over a network, instead of locally on a machine, runs the risk that performance will be impacted, drawing or otherwise. The point of the warning is to make a user aware that data is being accessed over a network, and that the user should probably check to see whether accessing that data over the network versus locally causes any performance problems. If a user checks and doesn't notice a difference or is willing to accept the difference, the warning hasn't been ignored. I strongly discourage users from ignoring the warning out of hand.

Re: Why Does Using a UNC Path Toss a Warning?

JoeBorgione — Tue, 28 Jun 2016 18:34:44 GMT

Obviously, I haven't ignored the warning; I understand what it's about now, and consider it a non-issue for me.

Re: Why Does Using a UNC Path Toss a Warning?

VinceAngelo — Tue, 28 Jun 2016 19:56:32 GMT

All access of data via network shares, either mounted or through a UNC is always slower. In my benchmarking on two different gigabit networks, it was a consistent 50% performance penalty. This has nothing to do with drawing (or even OS, since Linux had the same penalty). My benchmarks were with both ArcPy and the FileGDB API, and no draw operations were a part of the tests.Local filesystem access is always fastest (unless you're using a USB2.0 protocol thumb drive). I would recommend you evaluate the performance cost before considering it a non-issue.

Re: Why Does Using a UNC Path Toss a Warning?

JoeBorgione — Tue, 28 Jun 2016 20:55:47 GMT

But.... All my machines are now virtural. All my storage is on a san. How does one get away from traversing networks?

Re: Why Does Using a UNC Path Toss a Warning?

DanPatterson_Retired — Tue, 28 Jun 2016 20:58:39 GMT

You are stuck by the fact that you aren't the only user of the data.

Quit sharing

Re: Why Does Using a UNC Path Toss a Warning?

JoeBorgione — Tue, 28 Jun 2016 21:32:39 GMT

Actually, I'm the only GIS guy and the data in question is being consumed by an internal, third party application (connected on a fiber network). It's not like I have 200,000 AT&T iPhone users hitting the data and expecting a millisecond screen draw. The network guy sit down with me and we ran a few addresses through the CAD and the return was nearly simultaneous...

Re: Why Does Using a UNC Path Toss a Warning?

VinceAngelo — Tue, 28 Jun 2016 23:53:06 GMT

The use of network protocols is what causes the significant performance dropoff. I don't know why, but the difference is significant, and easily reproducible. I used 10k-1m row tables in my benchmarks, and the cost was always proportional with respect to row count (below 10k rows the millisecond timer started to have resolution issues on Windows platforms).

If the disk is "local" (seen by the operating system, as a non-networked "letter drive"), you will get better performance than by accessing a networked device, either as a letter drive or via a UNC path.

- V

Re: Why Does Using a UNC Path Toss a Warning?

JoshuaBixby — Wed, 29 Jun 2016 00:55:52 GMT

Interesting information, thanks for sharing.

Although not directly related, this reminds me of a discussion I had with some Microsoft folks quite a few years back now, around the transition from Server 2003 to Server 2008. The issue was a fairly significant performance degradation when a UNC path pointed to a file share on a local machine compared to a UNC path on a remote machine and especially when compared to I/O on the local file system(s). It seemed the Windows kernel or network redirectors were not designed, at that time, to bypass or short-circuit the network stack when a network path pointed to a local file system. This was in contrast to many Unix or Linux systems that would/could optimize that path through the system stack. This impacted our ArcGIS for Server deployments because the common practice in my organization back then was UNC paths for all data, local or otherwise. It would be fun to revisit that topic and do some benchmarking today, hopefully that problem is in the past, hopefully.

Of course local disk I/O is faster than network I/O, especially with SSDs coming on strong, but gigabit Ethernet is respectable. I guess the 50% performance penalty surprises me, a bit. Have you tested on 10GbE networks?

Re: Why Does Using a UNC Path Toss a Warning?

MichaelMiller2 — Wed, 29 Jun 2016 14:00:11 GMT

Vince,

Does this mean that you could assign an organization wide drive letter designation to a single share and it will perform faster than if we use the UNC for that share?

Re: Why Does Using a UNC Path Toss a Warning?

VinceAngelo — Wed, 29 Jun 2016 14:07:10 GMT

No, all networked drives are equally slow (which is why I specified "non-networked 'letter drive'")

- V