In response to Derek Ragona <[EMAIL PROTECTED]>:

> At 02:48 PM 8/24/2007, Peter Schuller wrote:
> >Hello,
> >
> >I have a Dell 2950 where my 7-CURRENT amd64 FreeBSD does not see all visible
> >memory. It has 4 GB of physical RAM. dmesg on boot includes:
> >
> >usable memory = 4280811520 (4082 MB)
> >avail memory  = 4117716992 (3926 MB)
> >
> >Yet summing memories visible in top yields ~ 2100 MB.
> >
> >Of note is that I have 6.2/amd64 on several other 2950:s with 4GB of RAM 
> >which
> >say on boot:
> >
> >real memory  = 5100273664 (4864 MB)
> >avail memory = 4122443776 (3931 MB)
> >
> >But has all 4 GB visible in top.
> >
> >Unfortunately I failed to notice this until after the machine has begun being
> >used, so I have limited possibilities for rebooting/mucking with BIOS
> >settings. I was hoping someone could suggest something right off the bat.
> >
> >In addition on the problem machine the following sysctl values are present:
> >
> >hw.physmem: 4280811520
> >hw.usermem: 3628220416
> >hw.realmem: 5100273664
> >hw.cbb.start_memory: 2281701376
> >hw.pci.host_mem_start: 2147483648
> >
> >With hw.usermem being slightly higher (but not 2 GB higher) on the 6.2 system
> >without a problem:
> >
> >hw.physmem: 4283285504
> >hw.usermem: 3998797824
> >hw.realmem: 5100273664
> >hw.cbb.start_memory: 2281701376
> >hw.pci.host_mem_start: 2147483648
> >
> >I was under the impression that memory visibility issues were a thing of the
> >past on amd64. Any insight?
> >
> >Thanks!
> >
> >--
> >/ Peter Schuller
> 
> You need to look closely at the hardware configuration for these servers 
> and their motherboards.  Often some memory is reserved for things like 
> onboard video, etc.  You can free up that video memory by adding a separate 
> video card, but necessarily other memory that may be used by the 
> motherboard.  Unfortunately with dell systems same model's don't 
> necessarily mean same motherboard.  Also, how memory is used via the BIOS 
> is dependent on the BIOS version.  You should try to be sure all systems 
> you want to compare have the same motherboard and chipset and that these 
> also have the same BIOS version.

Derek triggered a thought ... I believe the 2950s have the ability to
do "RAM RAID1", to increase RAM reliability.  If that belief is correct,
it could be that you've got 4G physically in the machine, but only 2G
logically available to the OS.

At least, I think I remember seeing an option like that in a BIOS ...

-- 
Bill Moran
http://www.potentialtech.com
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