Re: SSA Loop Verification Question (graphics)

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Date:         Fri, 25 Apr 2003 09:57:24 -0500
To: aix-l@Princeton.EDU

Thanks for your thoughts.

Indeed, all 5 nodes would need access to all disks at one time or another,
so it needs to stay in that mode. In terms of outages, this is just a
backup pool, so if there are hosts down, it is of no concern, unless if
course backups are running. We've never had an instance where there were 2
nodes down, but it could happen of course.

Thanks again,

Bill.
___________________________________________
Bill Verzal
AIX Admin/Komatsu America
(847) 970-3726 (v)

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  | Subject: Re: SSA Loop Verification Question (graphics) |
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I would switch the cables round on SAP80e, (swap A1 with A2; B1 with B2),
so
that throughout the loop, an A1 connects to an A2 etc. It'll work fine as
it is, but if you run a maymap or similar from SAP80e it will show the
disks
in the opposite order to one run on any other node. It's no extra effort
for you and may save future confusion.

Give some though to the bypass cards. I think you need to make sure that
the 1/16 and 8/9 cards are set to forced in-line, given that you've got so
many nodes in the loop.

Be aware that if you have two nodes down there is a risk of some disks
being
isolated. Unless you have a compelling reason to have one big, shared loop
I would strongly recommend splitting it up so that you have no more than
two
nodes in any one loop. Split drawers up if you need to, but that'll be a
lot less trouble than having so many nodes in the loop, in my experience.

Print some cable plans off, and trace the loops with various combinations
of
nodes down and bypass configurations. You might consider failures of SSA
drawers as well. I usually put the cable plan in a clear plastic sleeve
and
trace over it with dry-wipe pens in various colours.

If you need the single loop, an alternative configuration, (A loop only,
for
the front half of the drawers), would be to connect each node to ports 4
and
5, then run cables between the drawers from 8 to 1; similar for the B loop.
That way, if a node drops out the whole loop will remain intact, thanks to
the bypass cards. (Still need to keep the back and front discrete.) It
will even permit access to all disks when two or more nodes are down. The
downside is that it needs more cables.

Where possible, keep the disks for a particular node in the drawer to which
it is directly connected. That will help performance, and also make it
easier if you decide to split the loop later on. You probably don't have a
lot of choice with that at the moment, though.

Simon Green
Altria ITSC Europe s.a.r.l.

AIX-L Archive at http://marc.theaimsgroup.com/?l=aix-l&r=1&w=2
AIX FAQ at http://www.faqs.org/faqs/aix-faq/

N.B. Unsolicited email from vendors will not be appreciated.

> -----Original Message-----
> From: Bill Verzal [mailto:BVerzal@KOMATSUNA.COM]
> Sent: 25 April 2003 14:41
> To: aix-l@Princeton.EDU
> Subject: SSA Loop Verification Question (graphics)
>
>
> All,
>
> I have attached a JPG image of a proposed SSA loop
> configuration. I would
> like your feedback on it if you don't mind. Here is the scenario...
>
> I have (5) 7133-020 drawers and (5) hosts. There are 80 disks in the
> drawers (all 5 drawers are full).
>
> Currently, I have 36 devices in loop A and 52 in loop B (this
> is just the
> way it is now - I did not wire it up).
> Loop A is broken down 32 drives and 4 hosts (5 counting the
> host the map
> was drawn from).
> Loop B is broken down 48 drives and 4 hosts (5 counting the
> host the map
> was drawn from).
> After adding the last 8 drives I am getting
> SSA_DEGRADED_ERROR on my hosts.
>
> Please take a look at the JPG and offer your opinions.
>
> The goal of the proposed changes is to keep the front 8
> drives isolated
> from the read 8, as they contain different data. Currently,
> front and rear
> drives cross over all over the place.

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