On Fri, May 18, 2018 at 12:52 PM Tony Thigpen <[email protected]> wrote:
> For a little fun on Friday afternoon. > > We will be replacing our current VTL. > > The new VTL can be configured to look like 3490s or 3590s. Our current > VTL is defined to z/OS as 3490s. > > Some of the staff are saying: "All VTLs should be defined as 3490s > because that is what everybody does." > > Others are saying: "Let's make them 3590s because then they match the > few remaining physical 3590s and if we have an issue with the VTL we can > just swap the fiber and continue running on real 3590s until the problem > is fixed." > > It was suggested I ask here to see what others are doing. > We don't have that option here, we're stuck with 3490s. What I would consider is the average size of the data sets put on a virtual tape. And I don't know which VTL you are looking at, so I don't know how it works. My first thought is if you have a lot of multi-volume 3490 virtuals, it might be better to use 3590 as a base so that there are few virtual tapes changed together. The plus of this is easier tape management. The minus is that if the entire contents of a virtual tape need to be somehow "stage" onto a cache disk (like on our 3494-B10), then there is the "problem" of staging a singe 3590's contents into the cache; which will take longer than staging the contents of multiple 3490 virtual tapes on an "as needed" basis. Also the entire 3590 must remain cached until it is completely processed (or the job abends) whereas with multiple 3490s, when the job finishes with one 3490, the cache for that volume can be put on the release list and reused. This could be a serious consideration depending on cache size. Again, assuming that the VTL uses some sort of intermediate cache. Hum, I guess I arguing for 3490s based on: (1) reduced use of cache; (2) faster start to the job since less data needs to be copied into the cache. But if the VTL keeps all of the virtual tape data on disk and simply emulates tape access onto a disk file (no intermediate cache), then I'd go with 3590. > > Thoughts? > > -- > Tony Thigpen > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN > -- Once a government places vague notions of public safety and security above the preservation of freedom, a general loss of liberty is sure to follow. GCS Griffin -- Pelaran Alliance -- TFS Guardian (book) Maranatha! <>< John McKown ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
