[CentOS] [OT] NT5+ requires a LDM Disk Label ("Dynamic Disk") for software RAID -- WAS: IDE RAID support

[Bryan J. Smith]

Aleksandar Milivojevic <alex at milivojevic.org> wrote:
> On 2000 Pro and XP Home/Pro, the option is there, but
> either grayed out

What is your "Disk Label"?  "Basic" or "Dynamic"?

If you don't know, select:  
  Control Panel -> Administrative Tools -> Computer
Management
  Storage -> Disk Management

It will tell you either "Basic" (legacy BIOS/DOS pri/ext/log)
or "Dynamic" (LDM).

Microsoft does not allow you do to volume management on
"Basic" disks for the same reason I don't recommend people
use MD on the same (and recommend LVM/LVD2 instead, even
though MD is used for RAID-1 or RAID-5).  There is no way to
store meta-data pertinent to the RAID volume if you lose a
slice.  You _must_ use the LDM Disk Label to get _any_ volume
management in NT5+ (2000+).

> or there's popup screen informing you that it works only
> on Server and up (don't remember anymore).  You need to
> have at least Server version  of Windows in order to use
> it.

I don't know about XP Home, but I was fairly certain that
XP Pro does very much do at least spanned (no RAID), striped
(RAID-0, no redundancy) and, I believe, mirroring (RAID-1,
redundant).  RAID-5 (fka striping+parity) can only be on 200x
Server.

> Unless of course you managed to hack something in the
> registry to enable it (in which case you violated 
> licencing agreement, and sure, I'd like to know how you did
> it ;-). 
> Currently, the only software RAID option for 2000 Pro and
> XP Home/Pro are those fake RAID controllers with their 
> specialized drivers (I'm not aware of any 3rd party general
> purpuse software RAID drivers for Windows).

There are a few volume manager suites out there.  They are
typically for servers (and priced at such) though.

> Of course, all this holds only if Microsoft hasn't decided
> to unlock the feature in one of the service packs (which I
> doubt).

I think it's because you're not using a "Dynamic" disk.
It _will_ be grayed out then.  ;->

A quick search turned up the following MS KB articles:  

[NT5.1] Windows XP:  
  http://support.microsoft.com/kb/314343/  

Ah ha!  You are indeed correct!

"You cannot create mirrored volumes or RAID-5 volumes on
Windows XP Home Edition, Windows XP Professional, or Windows
XP 64-Bit Edition-based computers."

They _did_ take out "mirrored" support of the "clients" in
NT5.1!

Also note ...

"NOTE: Dynamic disks are not supported on portable computers
or on Windows XP Home Edition-based computers."

So XP Home can't do anything (I thought so, but wasn't sure).

Just for historical completeness ...

[NT5.0] Windows 2000:  
  http://support.microsoft.com/kb/175761/  

The LDM Disk Label (Dynamic Disk) was introduced with NT5.0.
It solved the serious issues that many people had with the
legacy BIOS/DOS Disk Label in "losing" RAID volumes back in
NT4.0 and earlier.

So Microsoft _did_ remove mirrored (RAID-1) as an option in
NT5.1 client OSes, from NT5.0.  Interesting.


-- 
Bryan J. Smith                 mailto:b.j.smith at ieee.org
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