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Sporadic SMB errors, Windows client to NAS file share

Hello,

Recently we have begun observing some SMB errors logging on our 2k12 R2 servers indicating a failure connecting to a share.  We have a NAS appliance servicing the share(s) in question via SMB3.  Thus far we have bee unable to identify an issue at either the client nor the server level, so it has been very frustrating.  

One thing I can say is that the issue only occurs sporadically and not on all machines, so my inclination is that it is something on the Windows side, but I'm just not certain.

Below is an example of the error.

The network connection failed.

Error: The transport connection is now disconnected.

Server name: \xxxxxxxxxxxxxx
Server address: xx.xx.xx.xx
Connection type: Wsk

Guidance:
This indicates a problem with the underlying network or transport, such as with TCP/IP, and not with SMB. A firewall that blocks port 445 or 5445 can also cause this issue.


Thanks in advance!
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blinkme323
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blinkme323
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Lawrence TsePrinciple ConsultantCommented:
That can be a lot of reasons.  Let's narrow down the possibilities.

1. Try to place another Windows Server 2012 R2 file server (even VM) and observe.  Can that problem be reproduced?

2. Are you using NetBIOS over TCP/IP?  
  > If your answer is "yes", do you have WINS server on both the WS2012R2 and NAS properly configured?

3. How do you locate your NAS?  via FQDN, IP address or NetBIOS name?  

4. Is your WS2012R2 have SMB Direct compatible NICs, and you have enabled SMB Direct?  If your answer is "yes", does your NAS has SMB Direct support too?

5. Have your try using Windows Performance Monitor to observe the underlying protocol layer (TCP/IP) for packet error or packet drop?
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blinkme323Author Commented:
1. We have tried to reproduce without success.  Very sporadic on only a subset of machines.

2. No

3.  The share is set up as a CNAME record that points to the NAS instance name

4. Can't speak on SMB Direct but SMB3 is in play and working elsewhere.

5.  Not yet, but that is probably next on our list

Also just for clarification, all of the 2k12R2 clients in this case are VMs.
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Lawrence TsePrinciple ConsultantCommented:
I have some recommendations here.  Don't know whether it can help but at least I will give them a try as my next step of troubleshooting:

1. Create an "A Record" in DNS for the NAS, instead of using CNAME.  Sometimes CNAME might not work as expected for some system, as we don't know how a system was implemented.  For example, if developer request the requested name identical to system name then everything is skewed up.  So, that might be required to have the "A Record" name to be specified in NAS OS too.

2. Since you are not using NetBIOS over TCP/IP, make sure you are accessing the NAS using the name "hostname.dnsdomain.fqdn", in FQDN format.  Of course if your Windows Client has "Append DNS Suffix" and the DNS suffix is accurate, that this step is not necessary.

3. You said VM, I am expecting your are talking about VMware VM.  If possible, try to test on Hyper-V VM or physical host.   If that's already Hyper-V VM then just ignore this point.

4. If you're talking about 2012R2 VM, I think you can ignore SMB Direct in most of the case.  Since up to this moment SMB Direct can be enabled in a VM, only when you are using SR-IOV and using Hyper-V as the underlying hypervisor, with SMB Direct hardware-capable NIC.

Cheers.
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