Dell Perc 6 disk geometry problem with RAID5 (both 6.3 final and 7.0 RC1)

John Baldwin jhb at
Wed Jan 23 06:49:43 PST 2008

On Sunday 20 January 2008 01:53:30 pm David Wood wrote:
> Hi there,
> In message <20080120175819.GA52965 at>, Erik 
> Trulsson <ertr1013 at> writes
> >On Sun, Jan 20, 2008 at 04:48:56PM +0000, David Wood wrote:
> >> In message <9c1614e00801200608k49195944mf241b7b0aa6a48 at>,
> >> Aldas Nabazas <freebsd.stable1 at> writes
> >>> We bought a new Dell PowerEdge 2950III with Perc 6/i and have the disk
> >>> geometry problem using 6.3 final or 7.0 RC1. Seems that we are not alone at
> >>> least one guy has similar problem reported earlier:
> >>> 
> >>>
> >>>0506.html
> >
> >I do not know if the mfi(4) driver has any problems with large disks, but it
> >is however well known that fdisk(8) and bsdlabel(8) (the tools normally used
> >to partition disks) have problems with volumes larger than 2TB.
> >
> >If you want to use volumes larger than 2TB then gpt(8) is the recommended
> >way to partition the disks.  It is however doubtful if the BIOS in your
> >system will allow you to boot from a gpt(8) parttioned volume which is
> >best solved with having a separate - smaller - boot volume where the OS
> >itself is installed.
> Erik's reminder is timely for those with >2TB volumes.
> You must use gpt and not fdisk on any disk, be it a single drive (in the 
> future, at least!) or a virtual disk on a RAID setup that are bigger 
> than 2TB. It may be wise to use gpt on any virtual disk that you might 
> grow to 2TB or larger in the future, so long as you're not needing to 
> boot from that virtual disk.
> fdisk will not work properly with 2TB and larger volumes - the MBR / 
> partition table setup can't cope with these large volumes.
> You can't boot from a GPT volume - that's a limitation of the BIOS 
> architecture. There is some thought about using EFI on x64 hardware in 
> the future (EFI is used on ia64 hardware; GPT is part of EFI), but we're 
> not there yet. This isn't just about adding GPT support to the BIOS - 
> the whole BIOS setup is wedded to MBR.
> If you need to boot from a >2TB array, create two virtual disks - one 
> smaller than 2TB to boot from (and use MBR on that), then the residue 
> can be GPT.

Actually, using gptboot in HEAD you can now boot from GPT on large volumes
(I've booted from a > 2 TB volume on a PERC5 using mfi(4) with it).  I
will see about getting that merged back to 6.x and 7.x in CVS.  We use
it for large volumes on 6.x and all volumes on 7.x at work.

> When I said there was nothing relevant waiting for MFC, I was aware of 
> the change that Tom mentioned, but that seems to be about Dell PERC 6 
> being identified as such rather than a MegaRAID. It doesn't seem that it 
> will change the behaviour of the driver in any way.

In our testing at work the 2950 rev 3's worked fine with mfi(4).

John Baldwin

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