Date:	Wed, 23 Jul 2008 22:46:48 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	Mike.Miller@...com
Cc:	fujita.tomonori@....ntt.co.jp,
	James.Bottomley@...senPartnership.com, Jens.Axboe@...cle.com,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: RE: [RFC PATCH] HP (Compaq) Smart Array 5xxx controller SCSI driver

On Tue, 22 Jul 2008 14:19:22 +0000
"Miller, Mike (OS Dev)" <Mike.Miller@...com> wrote:

> > -----Original Message-----
> > From: FUJITA Tomonori [mailto:fujita.tomonori@....ntt.co.jp]
> > Sent: Saturday, July 19, 2008 5:52 AM
> > To: Miller, Mike (OS Dev)
> > Cc: James.Bottomley@...senPartnership.com;
> > Jens.Axboe@...cle.com; linux-scsi@...r.kernel.org;
> > linux-kernel@...r.kernel.org
> > Subject: [RFC PATCH] HP (Compaq) Smart Array 5xxx controller
> > SCSI driver
> >
> > This is a SCSI driver for HP (Compaq) Smart Array 5xxx controllers.
> >
> > SCSI people can skip the following two paragraphs.
> >
> > Currently, a driver for HP (Compaq) Smart Array 5xxx
> > controllers is implemented as a block device driver,
> > block/cciss.c (aka, cciss). But the controller interface is
> > SCSI-3 compatible. The specification says, "A controller that
> > supports CISS is considered to be a SCSI storage array
> > controller". A scsi driver for the controllers was discussed
> 
> Not really. The only resemblance we have to a SCSI controller is the
> fact that we hang SCSI, SAS, and SATA drives off the backend. Our
> implementation of the SCSI spec is cherry picked for what we
> need. That, of course, could be changed.

The controllers support mandatory commands at least, as the spec says?


> > several times.
> >
> > I think that a SCSI cciss driver can be much simpler (and
> > maintainable) than the block cciss driver (the majority of
> > the code forging SCSI command can go away, we have the proper
> > sysfs entries for free, we can handle scsi tape drives easily
> 
> We already handle tape drives quite easily and one of these days I
> hope to satisfy Andrew to the point where he will accept my sysfs
> changes.

I think that there are other areas that we can improve with a SCSI
driver, such as error handling, queue depth management, etc.


> > etc). It would be helpful for distributions too since they
> > don't need stuff specific to cciss (such as udev rules).
> >
> >
> > There isn't any easy migration path for users. So I think
> > that we need to keep the block and scsi drivers for cciss for
> > some time (say two years).
>
> Precisely why I am luke warm to this proposal. Who's going to help
> customers decide which driver to use?

I guess that distributions (with HP) can, as they could with libata
vs. ide.


> What if a number of customers are happy with the block driver? Who
> will decide for them when to switch? What if a customer is using the
> block driver and unknowingly upgrades to the SCSI driver? He's dead
> the water at best, lost his data at worst.

I think that customers don't care about how the driver is
implemented. My point is that the SCSI cciss driver could be better
than the block one.

As James pointed out, we could provide a migration path; we can change
only the driver internal without changing the user-space interfaces:

With my SCSI driver (I uploaded a new one), I got the following
devices connected with my CCISS adapter:

clover:/home/fujita# lsscsi
(snip)
[3:0:0:0]    disk    HP       LOGICAL VOLUME   1.66  /dev/sde
[3:0:0:1]    disk    HP       LOGICAL VOLUME   1.66  /dev/sdf
[3:0:0:2]    disk    HP       LOGICAL VOLUME   1.66  /dev/sdg
[3:0:0:3]    disk    HP       LOGICAL VOLUME   1.66  /dev/sdh

I created symbolic links (neat udev rules can do automatically).

clover:/home/fujita# ls -l /dev/cciss/
total 0
lrwxrwxrwx 1 root root 8 2008-07-23 21:38 c0d0 -> /dev/sde
lrwxrwxrwx 1 root root 9 2008-07-23 21:39 c0d0p1 -> /dev/sde1
lrwxrwxrwx 1 root root 9 2008-07-23 21:39 c0d0p2 -> /dev/sde2
lrwxrwxrwx 1 root root 8 2008-07-23 21:38 c0d1 -> /dev/sdf
lrwxrwxrwx 1 root root 8 2008-07-23 21:38 c0d2 -> /dev/sdg
lrwxrwxrwx 1 root root 8 2008-07-23 21:38 c0d3 -> /dev/sdh

The symbolic links enable users to mount the device as before.

hpacucli seems to work (I didn't try all the commands but the point is
that we can provide the ioctl compatibility):

clover:/home/fujita# hpacucli
HP Array Configuration Utility CLI 7.80-3.0
Detecting Controllers...Done.
Type "help" for a list of supported commands.
Type "exit" to close the console.

=> ctrl all show config

Smart Array E200 in Slot 3    (sn: PA6C90L9SV90L0)

   array A (SAS, Unused Space: 0 MB)

      logicaldrive 1 (68.3 GB, RAID 0, OK)

      physicaldrive 1I:1:1 (port 1I:box 1:bay 1, SAS, 72 GB, OK)

   array B (SAS, Unused Space: 0 MB)

      logicaldrive 2 (68.3 GB, RAID 0, OK)

      physicaldrive 1I:1:3 (port 1I:box 1:bay 3, SAS, 72 GB, OK)

   array C (SAS, Unused Space: 0 MB)

      logicaldrive 3 (68.3 GB, RAID 0, OK)

      physicaldrive 1I:1:2 (port 1I:box 1:bay 2, SAS, 72 GB, OK)

   array D (SAS, Unused Space: 0 MB)

      logicaldrive 4 (68.3 GB, RAID 0, OK)

      physicaldrive 1I:1:4 (port 1I:box 1:bay 4, SAS, 72 GB, OK)


When HP and distributions think that the scsi driver is ready,
they can modify their udev rules for cciss and enable the SCSI driver
module instead of the block driver.


> > My scsi driver is still in an early stage (I tried to keep
> > the changes minimum). I can detect logical units, mount a
> > file system, do lots of I/Os, however, there are lots of
> > TODOs in the management features.
> 
> Have you taken into consideration any of the HP utilities and management agents? Those must work, period.

Yes, I understand that. We will need lots of tests.

As I explained, we can provide the compatibility of ioctl and device
names. We could avoid breaking the existing tools?

Even though we need lots of tests, I still think that migrating to the
SCSI subsystem is the right thing for CCISS in the long term
perspective.


> > If I can get an ACK from HP about the long-term migration of
> > cciss to SCSI, I'm happy to keep working on the SCSI cciss
> > driver and maintain it until HP takes over the driver.
>
> We already have a SCSI port of the driver that is at least as
> functional as you decribe. But I am against it's release for the
> reasons stated above. If we ever decide to release the SCSI port it
> should be developed by HP so we can be assured that the utils and
> agents work as expected. That doesn't mean we wouldn't leverage some
> of your work. ;)

If HP releases its SCSI driver, I'm happy to throw my driver away and
work on HP SCSI driver. I like to see a driver in development rather
than a finished driver; development in mainline rather than private
development at a vendor. Everyone can see the progress and try it.


Thanks,
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