Windows Azure Drive Overview

The Windows Azure Drive enables Windows Azure apps to use existing NTFS APIs for accessing a durable drive.   This can ease the pain in migrating  existing Windows apps to Windows Azure. Using Azure Drive, the app can read or write to a lettered drive letter (e.g., C:\) which represents a durable NTFS volume.  This drive is implemented as an Azure Page Blob containing an NTFS-formatted Virtual Hard Drive.

The Azure Page Blob can be mounted as a drive in Azure where all the non-buffered/flushed NTFS writes are made durable to the drive (ie the Page Blob).   In the event of a drive failure, the data is persisted via the Azure Page Blob  and can subsequently be remounted when the app instance is restarted. Alternatively it can be remounted elsewhere for a different app instance to connect to.   As the drive is an NTFS formatted Azure Page Blob, the standard blob interfaces are available for uploading  and downloading  NTFS VHDs to Azure.

The Windows Azure Drive can cache drive data on a local disk on the Virtual Machine .  Caching data on the local drive has the benefit of reducing  read traffic  to the page blob which will reduce transaction charges.    This is because, under the Azure billing system there are no additional charges incurred for reads made to the local disk cache, however charges are incurred for transactions against the Azure Page Blob.   Even when  caching is turned on,  non buffered and flushed writes are committed transactions to the Azure Page Blob in durable storage.

Whilst in Beta, Windows Azure Drive, is billed only by usage of the storage space consumed by the Azure Page Blob and the read/write transactions to the Azure Page Blob.

Related Articles:

• Windows Azure Drive Beta Launched [News]