Block IDs are strings of equal length within a blob.Block client code usually uses base-64 encoding to normalize strings into equal lengths.To create a page blob, you initialize the page blob and specify the maximum size the page blob will grow.To add or update the contents of a page blob, you write a page or pages by specifying an offset and a range that align to 512-byte page boundaries., writing a block or list of blocks to a block blob, appending blocks to a append blob, and writing pages to a page blob. Each version of the blob has a unique tag, called an , that you can use with access conditions to assure you only change a specific instance of the blob. When a blob is leased, only calls that include the current lease ID can modify the blob or (for block blobs) its blocks. For information about snapshots, see Creating a Snapshot of a Blob.Block blobs let you upload large blobs efficiently.When using base-64 encoding, the pre-encoded string must be 64 bytes or less.
If you don’t commit any block to this blob, it and its uncommitted blocks will be discarded one week after the last successful block upload.
Each block can be a different size, up to a maximum of 100 MB (4 MB for requests using REST versions before 2016-05-31), and a block blob can include up to 50,000 blocks.
The maximum size of a block blob is therefore slightly more than 4.75 TB (100 MB X 50,000 blocks).
New blocks remain in an uncommitted state until they are specifically committed or discarded.
Writing a block does not update the last modified time of an existing blob.