Re: Disk issue

[Larry Bolhuis <lbolhuis@xxxxxxxxxx>]

Neil, (Sorry about the name mixup last post!)

  More arms are good almost no matter how you do it. I would certainly
add 8s rather than more 17s. If you get enough arms in total then the
17s you currently have will be utilized less as the work is spread
across the new drives. Also since late last year the 10K RPM drives are
less money than the 7200 RPM versions so get those for sure.  Once
installed (and the system balances out) you should see that the 8G units
are somewhat less than twice as busy as the 4s because of the faster
speed of the units.  

  If you could swing it (which is not always possible) leave the 4s in
place and swap the 17s for more 8s.  This will help performance and
remove a potential I/O bottleneck. Or best case pull em ALL out and load
up on 10K RPM 8G drives across the board. (hey we can Dream can't we???)

  - Larry

"Carley, Neil" wrote:
> 
> Thanks guys for the reply, and now for the next bit of the equation :
> I'm drawing up a spec for upgrade (mainly DASD) and knowing that the 4gig
> disks are discontinued I was thinking about using the 8gig ones. The new
> disks will go into the main ASP also but would it be a bad idea to add a
> further different type of disk into the config ? I will be adding probably
> another 80+gig to our existing setup.
> Any further suggestions comments ?
> 
> thanks again for your advice on this matter
> 
> Neil
> 
> > -----Original Message-----
> > From: Larry Bolhuis [SMTP:lbolhuis@arbsol.com]
> > Sent: Monday, February 26, 2001 12:33 PM
> > To:   MIDRANGE-L@midrange.com; Carley, Neil
> > Subject:      Re: Disk issue
> >
> > Carley,
> >
> >   Amazing how the math works out here here just as it should! Let me
> > explain: Your 6607 drives are 4G units, the 6714's are 17G or just about
> > 4 times larger. Since they contain about 4 times as much of your 'stuff'
> > than the 4G units and are the same speed they will normally be about 4
> > times busier. (40% -vs- 10%)
> >
> >   This is why IBM (and many others) recommend against putting disks of
> > different sizes in the same ASP. Certainly this cannot be avoided
> > completely but you skipped one size (8.5G) in between and you can see
> > the problem it creates. If you were to get the 4G units up to 20% busy
> > (1/2 of recommended maximum) the 17G units would be around 80% busy!
> > (Twice recommended maximum).
> >
> >   Best thing you could do: Replace all of them with 10K RPM 8.5G drives.
> > OK, That's likely not practical (budget wise) but you may want to add
> > more arms to off-load those 17's as they are at the recommended maximum
> > utilization already.
> >
> >   Also at V4R4 and up there is a storage pool balance function that can
> > balance by access that may smooth this out for you some by putting
> > lesser used data on the 17G drives. (STRASPBAL).
> >
> >   HTH
> >
> >     - Larry
> >
> > "Carley, Neil" wrote:
> > >
> > > Hi,
> > >
> > > Hopefully someone can offer me some advice on this. I have a system here
> > > (720 V4R3) with 25 disks in the main ASP 18 x 6607's & 7 x 6714's. A
> > couple
> > > of weeks ago I noticed a few messages in qsysopr reporting problems with
> > the
> > > disks and recommending contacting service before any serious problems
> > > occurred, the machine was IPL'd that day and I have not seen any similar
> > > messages since. Using wrkdsksts I notice that the 6607's are only
> > running at
> > > about 10% busy whereas the 6714's are running at about 40% busy, is it
> > > normal to have two different types of disks running like this or could
> > this
> > > difference be causing a bottleneck on the system as we do tend to push
> > our
> > > system fairly hard ?
> >

-- 
Larry Bolhuis           | Cogito Ergo Vendo iSeries 
Arbor Solutions, Inc.   |
(616) 451-2500          |               (I think, therefore I buy iSeries.)
(616) 451-2571 -fax     |
lbolhuis@arbsol.com     |        #3  1951-2001
+---
| This is the Midrange System Mailing List!
| To submit a new message, send your mail to MIDRANGE-L@midrange.com.
| To subscribe to this list send email to MIDRANGE-L-SUB@midrange.com.
| To unsubscribe from this list send email to MIDRANGE-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---