John, Not only are Enterprise disk prices coming down, but virtualization gives z/OS shops access to Midrange disk drives which have a much lower unit cost. That's one of the reasons why HDS have gone into the Virtual Tape business with VTF (http://www.hds.com/products/storage-software/virtual-tape-library.html).
Using TMM or something like VTF means you can use all your standard Remote Copy software to replicate your tapes real time, across some pretty serious distances. And if you use RAID-6 then you can do away with duplexing altogether because the disk arrays can handle a double failure without data loss. Ron <SNIP> > With DASD prices now cheaper and still dropping, I > agree with you that there shouldn't be any need to write directly to tape. > > Why VSM/VTS and not HSM. Well, one reason is that handling duplicates in > HSM requires manual intervention. When a primary tape goes bad, you need > to > activate the alternate and then ensure that you produce another duplicate > of this tape. All quite simple, but still manual. When a virtual tape is > bad (due to a bad real physical tape), it's all handled under the covers > as > far as HSM is concerned. No need to screw around with primary and > alternate. You do need to invest more in the size of your VSM/VTS and > maybe > that is reason enough not to do this. > > Also, implementing high availability is a lot easier when the duplexing is > application independant. > > -- snip -- > > BTW: The biggest VSM/VTS advantage I in my opinion is the number of > drives. > It's important in multi-LPAR installation. > > -- snip -- > > That's true, but it is also important to size your VSM/VTS properly to > ensure that residency time is long enough for your virtual tapes and that > the tapes get migrated to the backend in a timely matter. > > John > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
