Windows Home Server “Vail” Drive Extender V2–New Features

Mark Vayman, a lead program manager on the Home and Small Business Server team just tossed out all the new features in Windows Home Server Drive Extender, version 2.  The information and discussion can be found in the Microsoft Forums, and I urge you to surf on over there and jump into the conversation with questions and comments.

Drive Extender is a storage technology first introduced in Windows Home Server's first release. The 1st generation of the technology was file based, and worked on top of "vanilla" NTFS volumes using reparse points. To address the customer feedback we have received and improve the system's resiliency to partial drive failures (seen many times by our support), the Drive Extender technology was updated to use block based storage below the file system similar to software RAID systems.

The following isn't an exhaustive list, but does try to enumerate the major new features as well as features which are no longer supported in the “Vail” version of Drive Extender:

Features carried over from the previous release:

• Duplication can be turned on/off per folder.
• Duplicated folders can survive a single hard drive failure.
• Storage pool can be easily expanded using different drive types and various sizes.
• Graphical representation of storage usage (AKA the pie chart) - isn't present in the beta, but is planned for the next milestone.

New/Improved features:

• For duplicated folders, data is duplicated in real time to two separate drives - there is no hourly migration pass.
• File system level encryption (EFS) and compression are now supported for Drive Extender folders.
• File conflicts are gone, duplication works as intended for files in use as it is performed at the block level now.
• The remaining amount of data to synchronize/duplicate is reported per storage pool.
• All storage operations are executed in the background without blocking other server operations. Specifically, drive removal can be issued without impacting the online state of shares.
• Drives in a storage pool can be named with a custom description to enable physical identification of the drive in the server.
• Drive serial number and exact connection type is reported for each drive.
• Drives which are bigger than 2TB can be added  to a storage pool.
• iSCSI storage devices can be added to the a storage pool.
• The system drive can be excluded from the storage pool.
• A new low-level storage check and repair diagnostic operation was added.
• All storage operations are performed with very low I/O priority to ensure they don't interfere with media streaming.
• A new "folder repair" operation is available which runs “chkdsk” on the folder's volume.
• To protect against silent storage errors (bit flips, misdirected writes, torn writes), additional information is appended to each 512-byte sector stored on drive. In particular, each sector is protected by a CRC checksum, which enables Drive Extender to detect data read errors, perform real-time error correction and self-healing (up to 2 bit errors per sector if duplication is disabled, and any number of bit errors if duplication is enabled) and report the errors back to the user and application. The overhead for this additional data is roughly 12% of drive space.
• Data drives in storage pools can be migrated between servers, and appear as a non-default pool.  A non-default pool can be promoted to a default pool if no default pool exists.

Deprecated features:

• A data drive from a storage pool cannot be read on machine not running the “Vail” server software.
• Data isn't rebalanced across drives to ensure even distribution. The data allocation attempts to keep drives evenly used. A periodic rebalance operation is considered for the next version.

Known inter-op/support issues with the Beta

• As with other software RAID solutions, Drive Extender isn't supported with BitLocker.
• Drive Extender cannot share the same drive with other software based RAID systems (such as Microsoft Dynamic Drives)
• Running low-level software storage tools—for example, defragmentation, full drive encryption, or volume imaging—on server folders may cause issues. These tools have not been fully tested in this release. Please avoid running these tools on the server.
• Internally, the “Vail” software has been tested with up to 16 hard drives and with up to 16 TB of total storage capacity. We’re aware of a number of bugs that occur beyond these limits, so please keep your beta installations under 16 drives and 16 TB total drive space.