Offline Files and Continuous Availability: the monstrous union you should not consecrate

The difference between Windows 8 and Windows 10

Windows 8.1 and Windows 10 support SMB3, allowing them to utilize CA, transparent failover, and Scale-out File Servers. But due to the aforementioned timeout problem that many customers reported, we decided in Windows 10 to fix the glitch.

Starting in Win10, when you connect to a CA-enabled share, there is no longer an option to use offline files. No matter the settings, files will not cache and the user will not run into timeout problems.

When you mark a share as “continuously available” you are essentially committing to the following contract:

1. The SMB server must always be available.
2. Any data written to the server needs durable persistence on disk and must be resilient to disk failures.
3. The network between the client and the server is expected to be fault tolerant and high speed.

The CA feature tries to hide transient failures at any of the above three interfaces from applications by holding and resuming handles. Remember, it’s for high-throughput, high-availability, high-IO, mission critical server applications like SQL Server and Hyper-V. #3 above directly conflicts with “offline files” – which assumes flakey, slow, and intermittent network connectivity.
Naturally, this decision to change the behavior in Win10 may not make your day, which leads me to:

A variety of alternatives

• Use Work Folders. The future is definitely Work Folders. CSC hasn’t had a feature update since Windows 8, and that should be a strong sign that it probably never will. We have moved into a new phase, where users want to sync their data from PCs, phones, and tablets – and not necessarily all running Windows nor SMB. Work Folders brings all that to the table, and is actively under development and accepting feedback. Heck, Jane the Work Folders PM wrote about it constantly. She never sleeps.

• Just use CA. If you are looking for data consistency and transparent failover for non-mobile users, stop using CSC. Disable it on all your CA shares using Server Manager, Failover Cluster Manager or Set-SmbShare:

• Just use CSC. If you are looking for mobile user and crumbling network support, stop using CA. Disable it on your shares using Server Manager, Failover Cluster Manager, Set-SmbShare, or Explorer:

• Use a two-share combination. If you have a hybrid set of mobile users and desktop users all accessing the same data, nothing is stopping you from creating two shares to the same data – one with CA enabled and one with CSC enabled. Then your users can select the share that matches their needs.

• Use OneDrive for Business & Sharepoint. There’s this whole bizarro world out there that doesn’t use file servers. I don’t truck with it, but you might find them interesting. Check out https://technet.microsoft.com/en-us/library/dn889837.aspx & https://onedrive.live.com/about/en-us/business/. I think some guy named Jose works there now. The traitorous swine.

The future

We heard the Windows 8.1 feedback and changed the behavior in Windows 10 to stop the timeout issue. We then had feedback from Windows 10 customers that wanted it back the old way. So we decided to add this ability back into a future release of Windows 10; look for it here in group policy:


Software\Policies\Microsoft\Windows\LanmanWorkstation\AllowOfflineFilesforCAShares