Posted by: tranquilpc | January 22, 2010

Safe Home Server – part 2

Safe_WHS

Drive Extender (DE)

Drive Extender – (wikipedia)

Windows Home Server Drive Extender is a file-based replication system that provides three key capabilities:
  • Multi-disk redundancy so that if any given disk fails, data is not lost
  • Arbitrary storage expansion by supporting any type of hard disk (SATA USB etc.) in any mixture and capacity — similar in concept to JBOD
  • A single folder namespace (no drive letters)

Users (specifically those who configure a family’s home server) deal with storage at two levels: Shared Folders and Disks. The only concepts relevant regarding disks is whether they have been "added" to the home server’s storage pool or not and whether the disk appears healthy to the system or not. This is in contrast with Windows’ Logical Disk Manager which requires a greater degree of technical understanding in order to correctly configure a RAID array.

Shared Folders have a name, a description, permissions, and a flag indicating whether duplication (redundancy) is on or off for that folder.

If duplication is on for a Shared Folder (which is the default on multi-disk Home Server systems and not applicable to single disk systems) then the files in that Shared Folder are duplicated and the effective storage capacity is halved. However, in situations where a user may not want data duplicated (e.g. TV shows that have been archived to a Windows Home Server from a system running Windows Media Center), Drive Extender provides the capability to not duplicate such files if the server is short on capacity or manually mark a complete content store as not for duplication.

 

It’s a great idea, and works beautifully to allow easy expansion / data protection for your files.  But in regard to the Safe Server, it makes like difficult, as the data (at least some of it) resides on the primary HDD (HDD1).  In the context of this series, this makes life extremely difficult, as you can’t ‘image’ the primary HDD as the data files will no doubt be changed, and not only the data but the data base of the files too – and that information is on the primary HDD.

 

The ‘industry alternative’ to Drive Extender is RAID (redundant array of inexpensive disks or more accurately Redundant Array of Independent Disks) – or specifically RAID 1 (mirror).  But this is not consumer friendly – needs specialised knowledge and constrains the HDDs you can use.  To learn more about DE vs RAID

 

Windows Home Server System recovery solution provided with all OEM Home Servers does ensure that even if the primary HDD fails you can restore and rebuild the current data – so there is no need to worry about your existing setup.

So – what is the solution ?

Next – the Safe Server Module.

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Responses

  1. […] Part 2 – Drive Extender (DE) […]


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