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.
