svn commit: r266242 - in stable/9: share/man/man4 sys/conf sys/dev/mrsas sys/modules sys/modules/mrsas

[Doug Ambrisko]

On Fri, May 16, 2014 at 09:16:15AM -0700, Bruce Simpson wrote:
| On 16/05/2014 08:46, Doug Ambrisko wrote:
| >   mrsas(4) attaches disks to the CAM layer so it depends on CAM and 
| >   devices show up as /dev/daX.  mfiutil(8) does not work with mrsas.
| 
| This is a big improvement. When using ZFS with mfi(4), mfiutil(8) can be 
| used to create an "un-RAID" configuration by creating several stripes 
| spanning single disks. The MegaRAID BIOS does not make the relevant 
| options easily available. Having native CAM support for each disk will 
| be a big help here.

Its not what you think.  The mrsas(4) driver attaches the logical volumes
or JBODs to CAM.  Now what you would want to do, to achieve what you want
is to create JBODs (not a RAID per drive) and then put each in your
ZFS pool.  With mfi(4) there was the cam passthrough option which gives
you raw access to the disk underneath the RAID controller.  So with
mrsas(4) /dev/mfid0 becomes /dev/da0 for example.  There is no equivalent
of mfi(4)'s /dev/da0 with mrsas(4).  It been reported that cam passthrough
in mfi(4) has troubles with some configurations.  This problem also happens
with mfi(4)'s JBOD since it uses passthrough mode.  It didn't happen
with mrsas(4) in JBOD so mrsas(4) is better there.  I can't repro. the
mfi(4) passthrough issue.

Newer RAID controllers should support JBODs so you don't have to
create the one RAID per disk.  I agree that this can be hard to
setup via the BIOS.  I haven't used storcli much.  It works with mrsas(4)
and is supposed to be better to use then MegaCLI.  I think I've created
JBODs with MegaCLi.  I recall you have to enable the JBODs feature via
MegaCli then you can create them.  I have created RAID volumes and JBODs
before at the same time on the same RAID contoller for testing.

We hope to extend mfiutil(8)/mrsas(4) to work together.  It would be
nice for mrsas(4) to create the /dev/mfid aliases so people could easily
switch between them if they are not used labels to access disks.  This
could help debug issues.

Thanks,

Doug A.