Dennis, You should be fine mixing sizes so long as you watch utilizations of individual volumes (particularly the smallest ones) and don't let any of them go over 50% full. We ran out of 3390-9 volumes a while ago and had to start adding 3390-27's for paging. Since they're all virtualized inside the storage array, device response times are pretty much all the same. When the 3390-9's get toward 50% full (or the high-water mark hits the end of the device - another thing I like to watch), I add some more 3390-27's. I pretty much disregard the aggregate page volume utilization, which is often less than 20% in our case.
Given that 240-248 puts you very close to the max number of page volumes, 3390-3's may not be the best choice because with a bit more growth, the only thing you'll be able to do is watch space utilization go beyond 50%, which won't be good. A place to start may be 120 3390-9's @ 33% util each. Then watch individual device response times to see if you need more actuators. Good luck! Mark Wheeler UnitedHealth Group -- "Excellence. Always. If Not Excellence, What? If Not Excellence Now, When?" Tom Peters, author of "The Little BIG Things" > Date: Wed, 29 Sep 2010 15:53:25 -0700 > From: dennis.l.o'[email protected] > Subject: Mixed page volume sizes > To: [email protected] > > On of our z/VM 5.4.0 systems is about to grow to 140 GB of storage. Given our > target overcommit ratio of 3:1, and IBM's advice to keep paging space no more > than 50% full, this should just about fit onto 240 or 248 3390-3 sized > volumes. My question is what will happen the next time we add storage. > Clearly, we'll have to start using 3390-9 sized volumes for paging. Would we > be better off converting only enough volumes to satisfy the space > requirement, which would maximize the number of devices, or should we convert > all volumes to 3390-9 to keep them the same size? My concern is that if we > mix sizes, CP will try to allocate the same amount of space on each volume, > and the 3390-3's will get more than half full. On the other hand, maximizing > the number of devices maximizes the number of concurrent I/O's. Our Storage > people aren't going to give me 240 3390-9's if I don't need them, so if I add > another 32 GB of storage, my choice would be something like 212 3390-3's and > 28 3390-9's, or 100 3390-9's. Which would be a better choice? > Dennis > > "Decision" is not a verb.
