Re: [PATCH 0/10] megaraid_sas: Updates for scsi-misc

[Douglas Gilbert <dgilbert@interlog.com>]

On 11-10-09 10:10 AM, James Bottomley wrote:
> On Sun, 2011-10-09 at 09:56 -0400, Douglas Gilbert wrote:
>> On 11-10-08 09:14 PM, adam radford wrote:
>>> James/Linux-scsi,
>>>
>>> The following patch series for megaraid_sas brings the driver up to v6.12-rc1:
>>>
>>> 1. Continue booting immediately if FW in FAULT at driver load time.
>>> 2. Increase default cmds per lun to 256.
>>> 3. Fix mismatch in megasas_reset_fusion() mutex lock-unlock.
>>> 4. Remove some un-necessary code.
>>> 5. Clear state change interrupts for Fusion/Invader.
>>> 6. Clear FUSION_IN_RESET before enabling interrupts.
>>> 7. Add support for MegaRAID 9360/9380 12GB/s controllers.
>>> 8. Add multiple MSI-X vector/multiple reply queue support.
>>> 9. Add driver workaround for PERC5/1068 kdump kernel panic.
>>> 10. Version and Changelog update.
>>
>> I haven't checked all SAS HBAs in Linux but of those that I
>> have checked only one doesn't support the SMP pass-through
>> in the bsg driver. And that HBA driver is megaraid_sas **.
>
> Technically the megaraid_sas isn't really a SAS HBA, it's a RAID one
> that just happens to have SAS/SATA disk attachments.  None of the RAID
> HBA's (including the IBM power raid) expose a BSG interface or even
> attach properly to the in-kernel SAS interfaces.

In JBOD mode MegaRaid SAS controllers are SAS HBAs
(marketing BS aside). Their firmware has the same
SMP pass-through as LSI's MPT SAS Fusion controllers.

There is no reason why a MegaRaid controller user
couldn't place a SAS-2 expander in front of an array
of disks and make some disks available to a MegaRaid
volume. Other array disks could be used by other
machines and the different sets could be isolated
from each other with SAS-2 zoning. The problem then
would be that via a MegaRaid SAS controller a user
could not monitor or control that zoning. Seems a
bit wasteful to add a "real" SAS HBA just to get
that capability.

Many SAS HBAs (including MPT SAS Fusion controllers)
do RAID 0 and 1 (and 10?) so they could be viewed as
"RAID" controllers that expose a BSG interface.

Doug Gilbert