PLEASE READ if you use the mfi(4) driver with a newer RAID adapter

[Sascha Wildner]

Hello,

Short story: The driver used for LSI Thunderbolt series RAID controllers  
will be switched to a different driver soon. Read on for more details. If  
you are unsure if your RAID controller is affected, you can check with  
'pciconf -l'. Search the mfi line(s) and check if there is  
"chip=0x005b1000". If you don't find this, you can skip this mail.

Following is a likely incomplete list of known adapters of this series.

* Dell PERC H810
* Dell PERC H710
* LSI MegaRAID SAS 9265
* LSI MegaRAID SAS 9266
* LSI MegaRAID SAS 9267
* LSI MegaRAID SAS 9270
* LSI MegaRAID SAS 9271
* LSI MegaRAID SAS 9272
* LSI MegaRAID SAS 9285
* LSI MegaRAID SAS 9286
* Intel RAID Controller RS25DB080
* Intel RAID Controller RS25NB008

THE PROBLEM:

There have been issues of data corruption with these cards and the mfi(4)  
driver. See http://bugs.dragonflybsd.org/issues/2683.

In the meantime, mrsas(4), a new driver supporting those (and later cards)  
has been imported that doesn't seem to have such issues. So now there is  
some overlap in supported cards between mfi(4) and mrsas(4) (namely,  
"Thunderbolt" series). The current default is to let mfi(4) grab them and  
there is a tunable (hw.mfi.mrsas_enable) which, if set, lets mrsas(4) take  
those cards. The intention of the tunable is to keep things running as  
before but offer the newer driver as an option.

The main difference when switching over to mrsas(4) is that the name of  
disk devices for the mfi(4) driver is mfiX while the mrsas(4) driver  
utilizes CAM and thus its disks are named daX. So just switching from mfi  
to mrsas might cause booting issues because /etc/fstab, /boot/loader.conf  
and /etc/rc.conf might all need to be edited because of the changed disk  
names. After that, it should work without issues. Also, mrsas(4) doesn't  
have a userland tool like mfiutil(8) yet.

But given that potential filesystem corruption is worse than potential  
booting issues (which can be fixed by editing the aforementioned files),  
we decided to switch the default for the cards supported by both drivers.  
This mail serves as an announcement that this will happen within the next  
two weeks or so.

WHAT YOU COULD DO NOW ALREADY:

If you want to prepare for the switch, it can be done now. Check the  
following files for occurrences of "mfid":

/etc/fstab         - as device name for filesystem mounting
/etc/rc.conf       - in dumpdev
/etc/loader.conf   - in vfs.root.mountfrom

These devices names will have to be changed to the appropriate daX name.  
Finding out this name in advance might be the tricky part because it  
depends on how many other (non-mfi) disks your system has and on the order  
of detection once mrsas(4) has taken over. If you are not sure, it might  
be easier to find out by enabling mrsas(4) temporarily. To do that, go to  
the loader prompt from the loader menu (type '9' in the loader menu) and  
do:

hw.mfi.mrsas_enable=1
boot

Once you have edited the files and it boots properly with the  
hw.mfi.mrsas_enable tunable, you can hw.mfi.mrsas_enable=1 permanently in  
your loader.conf. Once we make the switch, it will then become a no-op and  
mrsas(4) will be the default.

If there are any questions etc., by all means ask here, or mail me, or  
come to our IRC channel.

Sascha