Hardware RAID Support (was RE: One Last Plea For Vinum Assistance)

John john at starfire.mn.org
Thu Jan 20 05:57:31 PST 2005

On Thu, Jan 20, 2005 at 05:22:36AM -0800, Sandy Rutherford wrote:
> >>>>> On Wed, 19 Jan 2005 22:57:21 -0800, 
> >>>>> "Ted Mittelstaedt" <tedm at toybox.placo.com> said:
>  >   This did teach me a lesson that I kind of knew already but
>  > didn't think too much about.  That is, a software array is no substitute
>  > for a hardware array.  ...
> Agreed completely, which leads me to my question.
> Does anybody know what the plans are for the SCSI hardware raid
> controllers vis a vis CAM?  I have a Mylex Extreme RAID 1100, which
> uses the mlx(4) driver.  The mlx(4) driver does not use CAM, whereas
> its cousin the mly(4) driver does interact with CAM.  
> I corresponded with Michael Smith, the principal author of both
> drivers, a while ago and he told me that it was a pain in the neck to
> integrate mly(4) with CAM and he did not forsee this ever being done
> for mlx(2).  One side-effect of this is that although the RAID setup
> utility for the card does allow a channel(s) to be designated a plain
> non-RAID SCSI channel for use by a tape drive or CDROM, the FreeBSD
> driver does not support this.  Also, the mlxcontrol(8) facility is a
> little on the basic side, with most of the capabilities of the card
> not supported.
> My main point is that support for SCSI hardware RAID seems to be a bit
> of a dog's breakfast at the moment and are there plans to brings
> things together?
> BTW:
> 1. Please do not ask me to donate a card to the developers.  I don't have a
>    spare.  However, I know how the game is played and I am not asking
>    anybody to donate their time to my problems.  My only serious
>    problem was a bug in mlxcontrol, for which I submitted a PR, with a
>    patch.
> 2. If anybody is looking for a hardware RAID card, I can recommend the
>    Extreme RAID 1100.  It's a triple channel U2W card.  I got mine for
>    a song on Ebay.  Note that it is definitely worth the trouble to
>    update to the latest version of the firmware.

Sandy, there are Hardware RAID implementations that do not need
special controllers.  The array is free-standing, and presents
to the host what looks like simple disks, and hides mirroring,
RAID-parity, striping, scrubbing, and other integrity functions
behind that layer of abstraction.  I know that there are people
that are using such arrays as these (even EMC Symmetrix, which is
very costly) on FreeBSD systems, because FreeBSD just thinks that
they are just simple (but extremely fast and reliable:) ) disks.

Even CDW has such "under the covers" hardware arrays for sale.
You don't need ANY special support in FreeBSD to use some of them.

Be ware, though!  Some of them, for reasons beyond my ability
to phathom, do require custom HBA drivers!  That's right - 
standard HBA hardware and firmware - but custom drivers.
Maddening.  Make sure you understand what you are buying,
because FreeBSD probably won't be on their support matrix,
even though they will work find together.  That's nothing
new - FreeBSD is not on the support matrix of 90% of the
hardware we use.  Sadly, we're just not "on the radar screen"
for many of these companies.

FreeBSD has two problems in this regard - and if I were in a
decision-making capacity with a large company, I'd be donating
equipment and money to make these happen:
1) Some intelligent subsystems of this nature (EMC CLARiiON, EMC
   Symmetrix, Hitachi Thunder, LSI, Xiotech Magnitude) are moving
   to all FC-SW implementations, or at least, FC-AL, though FC-AL,
   whether "real" or "simulated" (QuickLoop simulates FC-AL on
   Brocade switches, for instance) does have some support in FreeBSD.
   FreeBSD's fibre support is, um, limited.  A driver has been
   written for QLogic controllers that use the "isp" chip, but it's
   not clear to me yet whether it supports FC-SW and FC-AL, or
   FC-AL only.  I can find some documentation that only mentions
   FC-AL, and other documetation that seems to hint otherwise -
   I'm actually in the process of trying to hook up an EMC CLARiiON
   through a Brocade switch to some Q-Logic cards now.  FreeBSD
   has no support for other FC HBA's.

2) FreeBSD does not have, as nearly as I can tell, any sort of
   path management software.  That is, there's no support for
   presenting the same volume down multiple HBA's and either
   coordinating the access or using one as active and the other as
   standby.  (Greg - if vinum does this, my apologies - I haven't
   seen what I recognized as this functionality.)  What I'm talking
   about here is like HP PV-LINKS, AIX MPIO, Veritas Volume Manager
   DMP (Dynamic Multi-Pathing), DG/EMC ATF (Automated Transparent
   Failover), or EMC PowerPath.  I think that Linux benefits
   from Veritas DMP (if you buy the license), but I'm not sure
   about that.

This message comes at a very interesting time.  I am, actually,
in a position to donate some FibreChannel switches, and I was
about to write to the author of the ISP driver to see if he,
or someone he knows, could put them to good use in the development
of any of thse functionatlities.

If anyone knows of anyone who could benefit from these resources
to advance FreeBSD, please let me know.

John Lind
john at starfire.MN.ORG

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