Re: 8G as a 4G replacement

Hi Chuck,

According to the AS/400 Redbooks......
The #2726 PCI Raid Disk Unit Controller supports a maximum of 15 one or 
two-byte disk units.  A minimum of four disk units of equal
capacity are required to implemnet RAID-5 protection.  A maximum of 10 disk 
units per RAID-5 array are supported.  Parity
information can be spread across four or eight disk units.  A maximum of three 
RAID-5 arrays are supported on one #2726.  Disk units
not supported in a RAID-5 array can be attached to the #2726 in wither 
unprotected or a mirrored environment.

Therefore.......
If I understand your situation correctly,  you should be able to ADD the four 
8.58 GB disks (as a RAID-5 array) to your AS/400 and
still have the option of adding another 4 disks as another RAID-5 array later.  
You should not see any performance problems with
this configuration.

However if you are REPLACING the six 4 GB disks with four 8.58 GB disks, you 
will see some performance decrease because you will
have fewer arms retrieving the information.

Good Luck!







                                                                                
                
                    Chuck Lewis                                                 
                
                    <clewis@iquest.net>        To:     MIDRANGE-L@midrange.com  
                
                    Sent by:                   cc:                              
                
                    owner-midrange-l@mi        Subject:     Re: 8G as a 4G 
replacement          
                    drange.com                                                  
                
                                                                                
                
                                                                                
                
                    01/08/01 02:53 PM                                           
                
                    Please respond to                                           
                
                    MIDRANGE-L                                                  
                
                                                                                
                
                                                                                
                



We are running a 620-2179 with 6 of the 4GB drives (6607's). We need to add more
disk and have been quoted for 4 of the 8.58GB drives...

I am CLULELESS on how this sets up. We have the 2726 Disk Storage Controller and
that is what the disk and the optical (CD) are on.

Is this (adding these drives) going to create a problem ? We need more storage
but is this going to hurt performance ?

Thanks !

Chuck

Larry Bolhuis wrote:

> > No way.
>
>   Rats.
>
> > This problem will continue to get bigger and bigger, and will particularly
> > plague customers in the future when the minimum disk size could potentially
> > grow to 17GB, 35GB and then 70GB if we follow the progression of where we
> > have been.
>
>   I certainly agree, many of the smaller systems out there already
> streached to get 4-4G units just to have RAID. 4-8G units when purchased
> new isn't so bad as the prices keep falling, but for the poor guy that
> want's to add 4G, he basically has to go used.
>
>   I think the biggest problem we will deal with is as Charly mentioned
> earlier: Arm count, or more correctly the LACK of arm count.  Already
> you can't cram enough arms in a 170 to feed the CPUs, how bad is it when
> we're pouring in 17G (or bigger) drives!
>
> > If you have a need for a 20 GB system, and the minimum DASD size is 70GB,
> > what do you do for protection.  In that case, the correct answer may be
> > mirroring.  BTW, mirroring will help with the arm contention problem.  But
> > what happens if you need with growth to have a system at 140 GB usable, and
> > the minimum disk size is 70 GB.  Raid-5 requires a minimum of four devices
> > in a parity set!
>
>   It is my opinion that IBM should continue to sell the smaller drives,
> even if they are just the larger ones with 'crippling' jumpers or
> microcode included (and I have told Mr Jarosh that for the good it'll
> do.) Heck, at this point even if they priced them THE SAME as the bigger
> drive the customer would save money. IBM has made good strides getting
> the entry level systems down in cost but then swat the poor customer
> across the face when they want 'just a little more storage'!
>
>   - Larry
>
> --
> Larry Bolhuis
> Arbor Solutions, Inc.
> (616) 451-2500
> (616) 451-2571 -fax
> lbolhuis@arbsol.com
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