How to disable local (on-disk) caching of cloud files by OS

Question

How to disable local (on-disk) caching of cloud files by OS

71861387 5

Hi,

In the context of sync provider built on top of windows cloud files API, we want to disable caching of data transferred to OS as part of placeholder hydration. In other words, once sync provider transfers the data as part of hydration during OnFetchData callback invocation, the platform should fulfill the client application read request with the data provided but should not store it on-disk as part of placeholder file. The sync provider will store the data in its own cache. Is it possible to configure platform for such behaviour ?

Thanks,
Nishit

Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2023-08-28T06:07:44.8033333+00:00

As far as I'm concerned, the OnFetchData (ReadFileEx) callback doesn't cache the data. See CloudMirror sample. The real transfer is done by CF_OPERATION_TYPE_TRANSFER_DATA.
71861387 5 Reputation points

2023-08-28T07:00:24.03+00:00

Right, the transfer is done by CF_OPERATION_TYPE_TRANSFER_DATA itself.
Looks like, platform already supports what i had asked for via CF_HYDRATION_POLICY_MODIFIER_STREAMING_ALLOWED flag https://learn.microsoft.com/en-us/windows/win32/api/cfapi/ne-cfapi-cf_hydration_policy_modifier. But, this does not work, even after using this flag, the placeholder file shows disk usage as non-zero post data transfer. Any idea ?

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Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2023-08-28T06:07:44.8033333+00:00

As far as I'm concerned, the OnFetchData (ReadFileEx) callback doesn't cache the data. See CloudMirror sample. The real transfer is done by CF_OPERATION_TYPE_TRANSFER_DATA.
71861387 5 Reputation points

2023-08-28T07:00:24.03+00:00

Right, the transfer is done by CF_OPERATION_TYPE_TRANSFER_DATA itself.
Looks like, platform already supports what i had asked for via CF_HYDRATION_POLICY_MODIFIER_STREAMING_ALLOWED flag https://learn.microsoft.com/en-us/windows/win32/api/cfapi/ne-cfapi-cf_hydration_policy_modifier. But, this does not work, even after using this flag, the placeholder file shows disk usage as non-zero post data transfer. Any idea ?

Answer 1

Xiaopo Yang - MSFT 12,731 Microsoft External Staff

CF_HYDRATION_POLICY_MODIFIER_STREAMING_ALLOWED
0x0002

This policy modifier grants the platform the permission to not store any data returned by a sync provider on local disks.

The flag does not work, and I can reproduce with CloudMirror.

please open an incident at link https://developer.microsoft.com/en-us/windows/support/?tabs=Contact-us and please choose the 'System Services Development - Cloud Filter API' for Windows SDK for this issue. In-addition, if the support engineer determines that the issue is the result of a bug the service request will be a no-charge case and you won't be charged.

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71861387 5 Reputation points

2023-08-28T10:51:30.66+00:00

Thanks for prompt response.

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How to disable local (on-disk) caching of cloud files by OS

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