PERC 6i and Incorrect drive size

[Harald_Jensas at Dell.com]

Hi Patrick,

You are seeing 512 MB less space available on each drive when using the PERC controller. This is because the PERC Controller use the DDF - Data Disk Format. 

DDF is a SNIA standard on how data is formatted on RAID Disk Groups. The standard specify that a minimum of 32 MB of space must be reserved on each disk in the RAID Group for the DDF structure. In the PERC case the designers decided to reserve 512 MB for the DDF structure, on each disk in the RAID group. I am not sure why, but I guess to be sure not to run out of space when new/more features are added. Another reason to go for such a large space is to make sure one can keep backward compatibility for a long time... etc.


You can read about DDF here:
http://www.snia.org/tech_activities/standards/curr_standards/ddf/SNIA-DDFv1.2.pdf


--
Harald Jensås

> -----Original Message-----
> From: linux-poweredge-bounces at dell.com [mailto:linux-poweredge-
> bounces at dell.com] On Behalf Of Elazar Broad
> Sent: 05 October 2008 05:20
> To: linux-poweredge-Lists; Boyd, Patrick
> Subject: RE: PERC 6i and Incorrect drive size
> 
> Hi Patrick,
>  Thanks for the reply. I am aware of that. My issue is more of how
> the PERC controller reports the drive size to the OS. Like so: If I
> plug one of the drives into the PowerEdge 1800's onboard CERC2/s
> controller, fdisk reports the drive as having 640.1GB/1,250,263,728
> sectors. On the other hand, fdisk on a PERC6i virtual disk(RAID1)
> reports 639.5GB/1,249,116,159 sectors. What I want to know is, why
> is there 500MB+ missing when using the PERC6i controller?
> Additionally, on a clean install of VMWare's ESXi the included
> partedUtil complains about the geometry reported by the
> controller's BIOS.
> 
> Elazar
> 
> On Fri, 03 Oct 2008 13:35:48 +0000 Patrick_Boyd at Dell.com wrote:
> >The drive manufactures measure drive size in base 10, i.e. a KB is
> >1000
> >bytes, a MB is 1000 KB, and a GB is 1000 MB.
> >
> >Software measures drive size in base 2, i.e. a KB is 1024 bytes, a
> >MB is
> >1024 KB, and a GB is 1024 MB.
> >
> >That is the discrepancy that you are seeing.
> >
> >-----Original Message-----
> >From: linux-poweredge-bounces at dell.com
> >[mailto:linux-poweredge-bounces at dell.com] On Behalf Of Elazar
> >Broad
> >Sent: Friday, October 03, 2008 3:27 AM
> >To: linux-poweredge-Lists
> >Subject: PERC 6i and Incorrect drive size
> >
> >I know this is slightly off topic. I have a PERC 6i in a PE1800, I
> >
> >have 2 WD 640GB drives connected to the controller. When booting,
> >if I hit Ctrl+R to access the configuration utility, both drives
> >only show as 609620MB as opposed to 640000. Any ideas are greatly
> >appreciated...
> >
> >Elazar
> >
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