Re: 'Device not ready' issue on mpt2sas since 3.1.10

[Robert Trace <maillist@farcaster.org>]

> I did some further research regarding my problem.
> It appears to me the fault does not lie with the mpt2sas driver (not
> that I can definitely exclude it), but with the md implementation.

I'm actually discovering some of the same issues (LSI 9211-8i w/ SATA
disks), but I've come to a slightly different conclusion.

I noticed that when my SATA disks are on a SATA controller and they spin
down (or are spun down via hdparm -y), then they response to TUR (TEST
UNIT READY) commands with an OK.  Any I/O sent to these disks simply
wait while the disks spin up and then complete as usual.

However, my SATA disks on the SAS controller respond to TUR with the
sense error "Not Ready/Initializing command required".  Any I/O sent to
these disks immediately fails.  You saw this in your logging:

> [  604.838640] sd 2:0:0:0: [sda] Device not ready
> [  604.838645] sd 2:0:0:0: [sda]  Result: hostbyte=DID_OK
> driverbyte=DRIVER_SENSE
> [  604.838655] sd 2:0:0:0: [sda]  Sense Key : Not Ready [current]
> [  604.838663] sd 2:0:0:0: [sda]  Add. Sense: Logical unit not ready,
> initializing command required
> [  604.838668] sd 2:0:0:0: [sda] CDB: Read(10): 28 00 00 00 08 00 00 00
> 20 00
> [  604.838680] end_request: I/O error, dev sda, sector 2048
> [  604.838688] Buffer I/O error on device md127, logical block 0
> [  604.838695] Buffer I/O error on device md127, logical block 1
> [  604.838699] Buffer I/O error on device md127, logical block 2
> [  604.838702] Buffer I/O error on device md127, logical block 3

Sending an explicit START UNIT command to these sleeping disks will wake
them up and then they behave normally.  (BTW, you can issue TURs and
START UNITs via the sg_turs and sg_start commands).

I've reproduced this behavior on the raw disks themselves, no MD layer
involved (although the freak-out by my MD layer is what alerted me to
this issue too... Having your entire array punted the first time you
access it is a little scary :-).  I'm also on raw hardware and I've seen
this behavior on kernels 3.0.33 through 3.4.4.

So, SATA disks respond differently depending on the controller they're
on.  I don't know if this is a SCSI thing, a SAS thing or a
firmware/driver thing for the 9211.

Now, whether or not the MD layer should be assembling arrays from
"failed" disks is, I think, a separate issue.

-- Rob