SUMMARY: Splitting a SW RAID array between two hosts

From: Tim Mooney <mooney_at_dogbert.cc.ndsu.NoDak.edu>
Date: Wed, 30 Apr 1997 20:24:24 -0500 (CDT)

All-

A few days ago I posted a number of questions on the feasability of splitting
a StorageWorks 410 RAID array between two machines in a non-dual-redundant
setup. The original question follows.

I received only one reply to my email (but I spoke with several different
people from sales and support last Friday, all echoing what Alan had to say)
from Alan Rollow, but he confirmed my suspicions that what we were trying to
do wouldn't work.

The essential answer to my question is that "the only way things could be
more screwed up is if we had ordered more hardware." :-) My boss has assured
me that he explained what we wanted to do and our current hardware in detail
to two different salespeople and both indicated our plans would work, but
after speaking with several more-knowledgeable people it's now clear that
things won't work.

In short:

1) It's *possible* (and it generally works pretty well) to split a RAID
array between two machines in non-dual-redundant mode *but* it's unsupported.
If something breaks, you're on your own.

2) If you do brave the waters and go with the unsupported configuration, you
*must* use the same type of controllers and same level of firmware on each.
You can *not* mix HSZ40s and HSZ50s in the same cabinet (this is a no-no
whether you're in a dual-redundant configuration or not).

3) If you do brave the waters and use the same type of controllers (i.e.
two HSZ40s or two HSZ50s, but not one of each) you do *not* need to segregate
RAIDsets on the internal buses of the array. It's fine to split a raidset for
one host across all six internal buses and do the same for a different raidset
for the second host.

3) The HSZ50 controller would have fit in the shelf in the bottom of our
SW410 -- in fact that's pretty much what the StorageWorks 450 array is.

4) The BA350-MB shelf we were told we needed obviously will not work in
our particular array -- the 410 (which is the same formfactor as the 450 and
the SW3xx arrays) was not designed to accept controller shelves -- it has
space for two controllers built into the bottom of the shelf and that's it.



We've since ordered an empty StorageWorks 450 desk-side cabinet, and we'll
be returning the BA350-MB shelf we have. We'll be yanking the extra disk out
of our 410 and putting it into our 450, and giving each of the two hosts in
question its own array, rather than making them share.

Tim

-- 
Tim Mooney                              mooney_at_dogbert.cc.ndsu.NoDak.edu
Information Technology Services         (701) 231-1076 (Voice)
Room 242-J1, IACC Building              (701) 231-8541 (Fax)
North Dakota State University, Fargo, ND 58105-5164
---------- original message ----------
All-
I've got some questions about sharing (splitting) a StorageWorks RAID array
410 between two hosts in a *non* dual-redundant configuration.  I'm hoping
someone else out there is doing what we intend to do with our array, and that
you might be able to point out any trouble spots with what we're planning.
We essentially want to have part of the array used by one host and another
part of the array accessed by another host, simultaneously.
We currently have the RAID array connected to a Digital Unix 3.2x machine.
There is currently one controller in the array, an HSZ40, configured like
such:
swxrc> 
Controller:
        HSZ40 ZG50100XXX Firmware V25Z-0, Hardware  A02
        Not configured for dual-redundancy
        SCSI address 7
        Time: NOT SET
Host port:
        SCSI target(s) (0), Preferred target(s) (0)
Cache:
        32 megabyte write cache, version 2
        Cache is GOOD
        Battery is GOOD
        Unflushed data in cache
        CACHE_FLUSH_TIMER = 65535 (seconds)
        CACHE_POLICY = A
swxrc> 
We have the bottom two (of the four) shelves in the 410 populated with drives,
and we currently have the bottom row as one RAID set (so the set is
split across all six of the internal SCSI buses), like this:
swxrc> 
Name          Type          Port Targ  Lun                    Used by
------------------------------------------------------------------------------
DISK100       disk             1    0    0                    RAIDS0
DISK110       disk             1    1    0                    SPARESET
DISK200       disk             2    0    0                    RAIDS0
DISK210       disk             2    1    0                    
DISK300       disk             3    0    0                    RAIDS0
DISK310       disk             3    1    0                    
DISK400       disk             4    0    0                    RAIDS0
DISK410       disk             4    1    0                    
DISK500       disk             5    0    0                    RAIDS0
DISK510       disk             5    1    0                    
DISK600       disk             6    0    0                    RAIDS0
DISK610       disk             6    1    0                    
swxrc> 
To connect the array to a second host, we've ordered an HSZ50 and a BA350-MA
controller shelf.
Now the questions.
1) We've been assured by various sales people that it's OK to mix HSZ40 and
HSZ50 controllers in the same array, but I'm still nervous about it.  Is
anyone doing this?  We plan to upgrade our HSZ40 to an HSZ50 sometime within
the next few months, but until we do that can we operate with two different
types of controllers in the same 410 array?
2) Since we're not operating in dual-redundant mode, I'm assuming that it's
not necessary that we keep the version of the firmware on the controllers at
the same level.  Is this a valid assumption?
We will be upgrading the firmware that's currently on the HSZ40 to version 3.1
(which we have), but the version of the firmware for the HSZ50 is at least
version 5.1, so it seems impossible to keep the firmware versions strictly
in sync.
3) The BA350-MA "User's Guide" mentions the StorageWorks 8xx and 5xx arrays,
but there is no mention of a 4xx array, like the 410 we have.  Based on what
I can tell from the "SWXSC-AA Office Expansion RAID Enclosure User's Guide"
that came with our 410, it appears very similar to the SW3xx cabinet.  The
410 comes with space within the card cage assembly for two controllers that
fit the HSZ40 form-factor.
It appears to me at this point like the BA350-MA controller shelf will *not*
work in the 410 array, and that the salesperson was wrong in telling my boss
that we needed a BA350-MA controller shelf for our array.  Can anyone
confirm this?
4) From what I can tell, the HSZ50 controller form-factor is very similar to
the HSZ40 controller form-factor, with the exception of the cache battery.
If my guess is correct and we *can't* use the BA350-MA shelf in our 410,
can we install the HSZ50 at all, or is the form-factor different enough so
that it will not work in the unused slot built into the bottom of the 410
array?
5) Assuming we somehow get to the point where we have two controllers in
our RAID array, would it be advisable to leave the *current* raidset as-is,
or would I be better off rearranging the raidset so that the original
controller has the raidset that is on the array's internal buses 1-3 (for
example) and the new controller has a raidset that is on buses 4-6?  What I'm
essentially asking is if it's wise to have both controllers simultaneously
using devices on all six of the internal buses, or if I would be better of
having one controller only use devices on certain buses and the other
controller only use devices on the remaining buses.
Thanks for any tips anyone can provide!
Tim
-- 
Tim Mooney                              mooney_at_dogbert.cc.ndsu.NoDak.edu
Information Technology Services         (701) 231-1076 (Voice)
Room 242-J1, IACC Building              (701) 231-8541 (Fax)
North Dakota State University, Fargo, ND 58105-5164

Received on Thu May 01 1997 - 03:36:14 NZST