New Driver for MegaRaid 6Gb/s and 12Gb/s Card

[Scott Long]

On Apr 19, 2013, at 12:44 AM, "Desai, Kashyap" <Kashyap.Desai at lsi.com> wrote:

> 
> 
>> -----Original Message-----
>> From: owner-freebsd-scsi at freebsd.org [mailto:owner-freebsd-
>> scsi at freebsd.org] On Behalf Of Matthew Jacob
>> Sent: Thursday, April 18, 2013 7:13 PM
>> To: freebsd-scsi at freebsd.org
>> Subject: Re: New Driver for MegaRaid 6Gb/s and 12Gb/s Card
>> 
>> On 4/17/2013 11:25 PM, Desai, Kashyap wrote:
>>> Hope my response clarifies your doubts. ~ Kashyap
>> No,  it doesn't.
>> 
>> What will happen if mrsas and mfi are both compiled into the kernel and
>> it boots on a system with the 1st thunderbolt?
>> 
>> It would be best to have one driver for the same hardware, period.
> 
> We are planning to move mfi and mrsas as loadable kernel module, once mrsas driver is submitted. With this, we will provide device.hint tunable option for customer to load mfi vs mrsas for Thunderbolt card.
> Best solution is not to have two drivers works with same hardware, but due to development cycle LSI added immediate support for
> Thunderbolt card in current mfi driver. Now we have new driver developed for the same card "mrsas".
> 
> Customer also wanted to provide choice between mfi vs mrsas for Thunderbolt card until they found "mrsas" is working fine without any major issue for them.
> LSI decided based on customer request and they did not wanted to force customers to use "mrsas" driver as immediate effect. There may be some customer who are using "mfi" driver in production environment and do not want to switch to "mrsas" if they upgrade FeeBSD kernel.
> 
> This provision of mfi vs mrsas priority is only temporary and in future, we should plan to remove Thunderbolt (Device ID 0x005B) from mfi because LSI will continue new development on "mrsas"

What will the exposed device names of the arrays be under the new driver?  Will it still be /dev/mfid* ?  If it's not, then this is where the problem lies.  Many users still use device names in their /etc/fstab for mounting all of their filesystems at boot.  If you have two drivers that will compete for the same hardware and give that hardware different names, they will break the fstab files for those users and they upgrade over time.  A similar situation occurred several years ago with the Intel e1000 driver; it was split into two drivers, with certain hardware that was supported by the old hardware going to the new driver.  That broke the network configuration for many users and caused years of pain and unhappiness as users upgraded and were hit by the switch.  We don't want that to happen here.

The real solution is that we need to have a single common naming convention for all disks (and for network interfaces), and leave the details of individual driver names out of the configuration part of the system.  That's not likely to happen any time soon.  The other solution is to mandate that users use volume labels for mounting their filesystems, but that's not likely to happen either, and even if it did, it present challenges for migrating existing users.  The only remaining solution that I can think of is to have the mfi and mrsas drivers share the same devclass for their disk interfaces (mfid*), but that's a hack that has not been fully explored in FreeBSD.  Still, I'd encourage you to try it and see if you can make it work.  If you have any problems, email me directly.

Scott