MFI and passthrough

[Doug Ambrisko]

Scott Long writes:
| Borja Marcos wrote:
| > On Nov 6, 2007, at 4:02 PM, Scott Long wrote:
| > 
| >> Doug Ambrisko wrote:
| >>> BTW, it works great in this mode if you know what you are doing :-)
| >>
| >> Can you explain what that means?  I recommend against it because it's
| >> not a well-tested configuration either in FreeBSD or in Dell.  It's not
| >> clear, at least to me, how basic things like i/o errors get handled; 
| >> does SCSI sense data get consumed by the controller firmware, or is it
| >> passed through to the OS without problem?
| > 
| > Aha, I see. I assumed that the controller would pass the sense data, 
| > etc, without problems.
| > 
| >>> | I do believe that Dell does sell a direct attached disk option for
| >>> | the 2950/1950 called the PERC5/e.  It's essentially an LSI MPT-SAS
| >>> | controller that directly replaces the PERC5/i card that you have now.
| >>> | It should be able to control all 6 disk slots, and can do both SAS
| >>> | and SATA.
| >>> I've been told the PERC5/e and PERC5/i are the same except for PCI
| >>> sub-device ID and are both the mfi(4) RAID controllers.  They do
| >>> have a mpt(4) based card but it only supports 4 bays.  I'm not sure
| >>> what it's real name is but we have some lying around for random
| >>> testing.  I don't leave them in machines.
| >>
| >> We should get a definitive answer on this.
| > 
| > We asked our Dell salesman and he confirmed that there's a non disk 
| > array card for this machine,
| > but it only supports 4 disks, not 6.
| 
| Ok, I thought that the 4 disk option just routed the motherboard SATA 
| connectors to the backplane, and that there was a 6 disk SAS+SATA option 
| that put an MPT card into the slot behind the backplane.  Oh well.

The Dell storage cards are interesting now.  The built-in cards are
a PCIe card on a horizontal tray the plug in a special PCIe slot by
the front.  You can take it off the tray, screw on a PC slot bracket
then plug it into a PCIe slot.  So the same cards can be used for
either in the special slot in the PE2950 or in the other Dell machines
via a generic PCIe slot.  The mpt(4) card only has on SAS connector
on that can only plug into one of the SAS back-planes connector.  So
you are limited to 4 SAS bays.  The mfi(4) cards have 2 so you can
use all drive bays.  Dell's current mpt(4) and mfi(4) cards have been
layed out so they can be interchanged with their mounting HW.  The only
this I don't know is their naming since PERC is for "built-in" and CERC
is external.  Also I'm not sure what they do for the battery if in
generic PCIe mode.  They could make a battery that bolts on or piggy
back the DIMM like LSI does.  I don't know all of the specifics since
we order random things that I just make work.  It's a fairly smart move
since they can offer the same RAID/SAS stuff across their product line
and only use 2 cards.  Since they share the SAS card and some platforms
don't have the space for a lot of drives they probably cost reduced it
to one connector versus the 2.  Note moving cards around like this is
probably not supported but I do things like this to test out things.

Doug A.