When you upload data, your client divides that data into blocks and uploads each block individually. Each block that is upload is billed as a _write_ operation. A final write operation is needed to assemble blocks into a blob that is stored in the account. The number of write operations required to upload a blob depends on the size of each block. **8 MiB** is the default block size for uploads to the Blob Service endpoint (`blob.core.windows.net`) and that size is configurable. **4 MiB** is the block size for uploads to the Data Lake Storage endpoint (`dfs.core.windows.net`) and that size isn't configurable. A smaller block size performs better because blocks can upload in parallel. However, the cost is higher because more write operations are required to upload a blob.
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