PE 4600: Splitting backplane - daughter card, please help!

Sites, Brad BSites at
Fri Oct 17 14:08:14 CDT 2003

Karthik Viswanathan wrote:
> Matt, Jessica,
> Thanks for your reply.
> Matt, I already have the system with the specification I had
> mentioned. I wanted to add the daughter card to it to get 2x4
> configuration (not 2x8 as u corrected !) I dont want to set the two
> 146G hard disk in a raid setup since I have only two 146G hard disk
> and cannot afford to lose half by setting in raid 1, also not ready
> to take risk of putting in Raid 0.

Not sure what "risk" you are talking about.  If you trust the card to do
RAID5 why wouldn't you trust it to do RAID0?  If you are getting good
backups of the files, there is no "risk" that you talk about.  In some
peoples opinions (mine included) you would actually have more efficient use
of the drive space by combining them.

> So as far as I understood from
> jessica and your message is, all I have to do is get a daughter card,
> spit the backplane and fix the 3x18G hard disk to one array and set
> it in RAID 5 and fix the 2x146G hard disk to other array (without any
> raid setup).

Just for clarification, an array us usually a set of disks put into a
collection that act as one.  So, if you aren't doing any RAID with the two
146GB drives, they would not be an array.  They would simply be two SCSI
disks.  I think the better way to look at this is that the backplane would
be split into two channels.  The three 18GB drives would be connected to one
channel while the two 146GB drives would be connected to the other channel.
If the three 18GB drives are put into a RAID5, they would be an array (hence
the acronym RAID = Redundant Array of Independent Disks).

> And as far as the cabling goes, There should be two SCSI
> cables running to the backplane from the system board, one for the
> first array(18G) and other for second array(146G). Also there should
> be a cable running from the perc3/dc card to the 18G array for
> setting in RAID 5. Did I understand correct?

This is close.  There will only be two cables running from the RAID
Controller to the backplane.  One for the first channel and one for the
second channel.  There is no separate cable for the RAID capability.
However, I'm a little confused by your configuration.  From your earlier
email that showed the listing, I don't remember seeing anything about RAID
except for the PERC3/DC which is an add-in card.  If that is really the
case, then the two cables for the split backplane would come from the add-in
card and not the system board.  The two channels on the system board would
be SCSI only and would not be connected to the backplane in this scenario.

> As I had mentioned
> earlier, there is a tape drive attached and I guess it is a SCSI
> drive. If so, how can I connect the SCSI cable to this. I would
> prefer to keep this in the same channel as the 146G hard disk is. Is
> it possible?

This all depends on how your system is really configured.  If you have the
146GB drives connected to a RAID controller (via the split backplane), then
it is not advisable to have the tape drive on the same channel.  Someone
correct me if I'm wrong, but everything I have been taught says that you
should not have a tape drive on a RAID enabled channel.  I think Dell even
says that this is a no-no.  But, if you are just using a plain SCSI channel
for this half of the backplane, then it would be possible to have the tape
drive on that channel along with the drives, however, you are gonna have to
find the right cabling to go to the tape drive first and then from that to
the backplane, because the backplane has to be the last thing on the cable
since there is no "through/out" connector.  But, since it looks like you
have the add-in RAID controller, then I would suggest using that for the
backplane and using one of the on-board SCSI channels for the tape drive.

I will reiterate Matt Domsch's suggestion of talking to a System Consultant
at Dell for the final verdict on all of this.  They are very capable people
and will be able to pull up your system configuration in the system to see
what you really have in your 4600 and can guide you on how to re-configure
it to meet what you want.  I would work through your Dell salesperson to get
this done and they can get the order placed for the correct parts, if
needed, based on the engineer's help.

Just my opinions and thoughts.  Take them as you will.  Hope it sheds some
additional light on things.

   .~.    Brad Sites
   /V\    Systems Administrator
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