> ## Documentation Index > Fetch the complete documentation index at: https://docs.nebius.com/llms.txt > Use this file to discover all available pages before exploring further. # How data transfers work in Nebius AI Cloud *Data transfers* allow you to move data between buckets. You can use a data transfer, for example, when you need to replicate and back up your data in a bucket, or when you want to migrate from a different region or third-party storage service. Data transfers support both Object Storage in Nebius AI Cloud and S3-compatible third-party services as sources and destinations. For more information, see [Bucket requirements for data transfers](/object-storage/transfer/requirements). You can manage data transfers in the web console or by using the CLI or the provider for Terraform. For instructions, see [Launching transfers](/object-storage/transfer/launch) and [Managing transfers](/object-storage/transfer/manage). ## Iterations Data transfers consist of consecutive *iterations*. Each iteration passes the source and destination buckets once. At each iteration, Object Storage performs the following operations in parallel: * Lists objects in the source bucket by making a `ListObjects` request for every 1000 objects. For every listed source object, Object Storage makes `HeadObject` requests to both the source and destination buckets, and then determines which objects need to be transferred: * If you allow [overwriting destination objects](/object-storage/transfer/destination-objects#overwriting-destination-objects), a source object that is newer than its destination pair (based on the `Last-Modified` header) overwrites it. If you also allow [overwriting unmanaged objects](/object-storage/transfer/destination-objects#unmanaged-destination-objects), the same applies to objects in the destination that weren't copied from the source bucket during the current or past transfers. * After the first successful iteration, source objects that were last modified before the last successful iteration are skipped to reduce synchronization costs. * If the source and destination objects have identical data but different metadata, Object Storage doesn't transfer the object data again. Instead, it updates the destination object's metadata by making a `CopyObject` request with `MetadataDirective` set to `REPLACE`. * If [deleting destination objects](/object-storage/transfer/destination-objects#deleting-destination-objects) is enabled, Object Storage lists objects in the destination bucket by making a `ListObjects` request for every 1000 objects. Object Storage compares source and destination object lists, determines which destination objects don't have pairs in the source, and deletes them using `DeleteObject`. If [overwriting and deleting unmanaged objects](/object-storage/transfer/destination-objects#unmanaged-destination-objects) is disabled, Object Storage doesn't delete destination objects that weren't copied from the source bucket during the current or past transfers. * For every object that needs to be transferred: * If the object is less than 100 MB, it makes a single `GetObject` request to the source bucket and a single `PutObject` request to the destination bucket. * For larger objects, it makes the following requests: 1. `CreateMultipartUpload` to the destination bucket. 2. `GetObject` to the source bucket and `UploadPart` to the destination bucket for every approximately 50 MB of the object. 3. `CompleteMultipartUpload` to the destination bucket after uploading all parts. The same logic applies to [blobs](https://learn.microsoft.com/en-us/azure/storage/blobs/storage-blobs-introduction#blobs) in Azure Blob Storage containers, regardless of the type of blob. ### Number of iterations and empty iterations You can configure a data transfer to stop after one iteration or after a number of consecutive empty iterations or to continue indefinitely. An *empty iteration* is an iteration where no data is transferred or deleted. To configure the number of iterations, choose a data transfer type in the web console or define a stop condition in the developer tools, such as the CLI. For transfers with more than one iteration, you can also set the interval between iterations. For more information, see [Data transfer types and stop conditions](/object-storage/transfer/stop-condition). ## Costs The cost of a data transfer consists of the costs for the source and destination buckets. The data transfer itself doesn't incur additional costs. | | **Destination: Nebius** | **Destination: external** | | - | - | - | | **Source: Nebius** | | | | **Source: external** | | *Not supported* |