azure-storage-azcopy-sync-guidelines.md

author	normesta
ms.service	storage
ms.topic	include
ms.date	02/09/2023
ms.author	normesta

By default, the sync command compares file names and last modified timestamps. You can override that behavior to use MD5 hashes instead of last modified timestamps by using the --compare-hash flag. Set the --delete-destination optional flag to a value of true or prompt to delete files in the destination directory if those files no longer exist in the source directory.

• If you set the --delete-destination flag to true, AzCopy deletes files without providing a prompt. If you want a prompt to appear before AzCopy deletes a file, set the --delete-destination flag to prompt.

• If you plan to set the --delete-destination flag to prompt or false, consider using the copy command instead of the sync command and set the --overwrite parameter to ifSourceNewer. The copy command consumes less memory and incurs less billing costs because a copy operation doesn't have to index the source or destination prior to moving files.

• If you don't plan to use the --compare-hash flag, then the machine on which you run the sync command should have an accurate system clock because the last modified times are critical in determining whether a file should be transferred. If your system has significant clock skew, avoid modifying files at the destination too close to the time that you plan to run a sync command.

• AzCopy uses server-to-server APIs to synchronize data between storage accounts. That means that data is copied directly between storage servers. However, AzCopy does set up and monitor each transfer, and for larger storage accounts (For example, accounts that contain millions of blobs), AzCopy might require a substantial amount of compute resources to accomplish these tasks. Therefore, if you are running AzCopy from Virtual Machine (VM), make sure that the VM has enough cores/memory to handle the load.