The File Director Windows client performs delta syncs on uploads and downloads where a portion of a file has changed.
The File Director client keeps signatures for synchronised files (which are generated after a successful upload or download) in order to allow the sync engine to generate a delta or a patch. For performance reasons these signatures are cached for the lifetime of a user’s session in the dn_signatures directory in the user's temp directory (%temp%). The relationship between these signature files and the file from which they were generated is stored in the client’s in-memory cache of the File Director files and cannot be derived from looking at the signature files themselves.
If a delta sync is interrupted, it will be restarted from the beginning.
For a delta upload to take place, the following must be true
- The Map Point must reside on an SMB share
- Only the Windows client currently supports delta syncing
- The file must exist locally and remotely
- The file must not be excluded from delta syncing via the exclusion mechanism - see Configuring Exclusions and Electives in the DataNow Windows Client
- The file must be larger than 4k (or the delta sync threshold if modified by the UploadFileSizeDeltaThreshold Reg DWORD in HKLM\Software\AppSense\DataNow)
Delta syncing is useful for minimising the network transfer required, which is desirable over a contended link to avoid impact to other line of business applications. There is a CPU cost however at both the client and server side to generate and decode signatures. If available bandwidth is abundant and increased server density / client performance on low spec endpoints is desired, excluding files from delta sync is an option. Typically the performance impact to an endpoint is minimal, since users typically only save changes to a file at a time - bulk changes to local content is rare unless performed by an application, and in this case it is recommended to exclude transient files from syncing altogether for best performance.