[CentOS] Centos 4.4: Support for Dell PowerEdge 830 CERC 6-Channel SATA RAID Controller

[Rodrigo Barbosa]

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Note: There IS an authoritative answer on this e-mail. Be patient with
me, please :)

On Wed, Sep 13, 2006 at 11:14:20PM -0500, Erick Perez wrote:
> Does Centos/RHEL 4.4 supports the CERC 6-Channel SATA RAID Controller
> that comes with the Dell PowerEdge 830 Tower Server?

CERC meaning "Cost Effective Raid Controller", which doesn't bode well.

According to Dell[1]:

[QUOTE]
CERC SATA 2S

The CERC SATA 2S RAID controller is a combination BIOS and driver-based 
software RAID solution, which uses the system motherboard's SATA controllers. 
It is not a hardware RAID solution such as the aacraid and megaraid 
controllers listed above.

Systems with this controller include the PowerEdge 800, SC1425, and 420SC.

Under Windows and Netware, there are special device drivers which operate in 
conjunction with the system BIOS to present the system SATA disks as a RAID 
volume.

Under Linux, the disks should be treated as two independent disks, which use 
the standard Linux "MD" software RAID layer for RAID 0 or 1 operation (if 
you so desire). System Documentation on support.dell.com[2] describe how to 
configure the system BIOS to either disable the RAID mode, or to set up the 
disks as two independent RAID volumes (effectively disabling the BIOS software 
RAID feature). 
[/QUOTE]

Notice: "It is not a hardware RAID solution". Also notice this might not
be the controller you have.

On the other hand, some people claim otherwise[3]:
"I did some digging this AM and everything points to it being a MegaRAID 
SATA 150-6 card (...)"

You might also take a look, subcribe or ask questions on the
linux-poweredge mailing list[4]. That might be the best place to
get help on this issue.
This[5] particular post seems promising.

This last page[6] seems to indicate that it is really a magaraid-like
controller, even providing a software to monitor it.

Of course all of that is very instructive, but doesn't give you an
authoritative answer. Where should we look for that ? The kernel source,
of course ("Use the source, Luke!").

The file drivers/scsi/aacraid/linit.c can be very instrutive on this particular
case. On line 136 (or thereabout), you will find:

        { 0x9005, 0x0285, 0x1028, 0x0291, 0, 0, 38 }, /* CERC SATA RAID 2 PCI SATA 6ch (DellCorsair) */

And on line 211 (or thereabout):

        { aac_rx_init, "aacraid",  "DELL    ", "CERC SR2        ", 1 }, /* CERC SATA RAID 2 PCI SATA 6ch (DellCorsair) */

	So we have a CERC SATA RAID with 6 channels from Dell, which really
looks like the one you are talking about. It gets identified as CERC SR2,
and is supported bu the aacraid driver. The only question left is, does
this support exists out of the box on CentOS (4.4) ? Lets ask the module,
of course. On /lib/modules/2.6.9-42.0.2.EL/kernel/drivers/scsi/aacraid, we
can check it:

# strings aacraid.ko | grep CERC
CERC SR2        

	There you go. Sorry for taking so much space to answer your question,
but I'm hoping you can use my reasoning here for other things as well.

References:
1 - http://linux.dell.com/storage.shtml
2 - http://support.dell.com/support/edocs/systems/SC1425/en/index.htm
3 - http://www.linuxquestions.org/questions/showthread.php?t=336615
4 - http://lists.us.dell.com/pipermail/linux-poweredge/
5 - http://marc.theaimsgroup.com/?l=linux-poweredge&m=112783948009432&w=2
6 - http://www.deadcat.net/search.php?action=browse&sectionid=16

- -- 
Rodrigo Barbosa
"Quid quid Latine dictum sit, altum viditur"
"Be excellent to each other ..." - Bill & Ted (Wyld Stallyns)

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