Esmie, If you choose to compress them then they are compressed. This is the common practice. Ml1 is often the same media as Primary, so compression is where one would save space and cost with ML1. It is why one typically gives compressed datasets a management class that bypasses a period on primary and sends them to ML2.
Many sites choose to have ML2 uncompressed as this is already performed by the tape media, just like you would with DFSMSdss. This saves CPU, but means the channels are busier. The saving for ML2 is archiving the datasets on media with a cheaper TCO. If you move ML2 to disk you should look at whether compression has to be enabled again and figure that into your current CPU profile. If you were to go with an ML1 only strategy or simply use ML2 Disk, I would suggest investigating the potential savings of using internal SATA drives, or if you are using HDS USP or USP-V look at using virtualized midrange storage - HDS or non-HDS midrange. Depending on when you run primary and secondary space management, there may be the potential to figure some CPU capacity savings by using cheaper disk media, leaving compression off for ML2, and turning it off for ML1. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of > esmie moo > Sent: Wednesday, April 21, 2010 5:45 AM > To: [email protected] > Subject: Re: [IBM-MAIN] DFHSM QUESTION - MOVING TO DASD FROM TAPE - ML2 > > Ron, > > You mentioned compression. Please correct me if I am wrong. All the dsns on > ML1 are compressed? > > Thanks. > > --- On Tue, 4/20/10, Ron Hawkins <[email protected]> wrote: > > > From: Ron Hawkins <[email protected]> > Subject: Re: DFHSM QUESTION - MOVING TO DASD FROM TAPE - ML2 > To: [email protected] > Received: Tuesday, April 20, 2010, 12:46 PM > > > Darth, > > The ML1 and ML2 are usually cheaper and lower performance than Primary > Storage. ML1 cost efficiency is usually achieved through compression, > whereas ML2 is a change in media. > > ML2 Tape can easily be replaced with Tier 2 disk using internal SATA, > external virtualized midrange storage, or earlier generations of DASD disk > systems with a reduced maintenance cost (I think Radoslaw did this with > 7700E). > > Ron > > > > > > > > > If I understand this correctly, you're going to have 2 levels of migration > > both on Disk? Even if that's possible, what does it gain you? Wouldn't > > it make more sense to just have an ML1 and then no ML2? And again, I > > question whether that's even possible with HSM. > > > > I do seem to remember this same discussion in the past, so you should > > probably check out the archives. We're actually going the other route - > > we're moving to a 'tapeless' virtual tape system & I'm eliminating ML1. > > > > ddk > > > > ---------------------------------------------------------------------- > 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 > > > > > ---------------------------------------------------------------------- > 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 ---------------------------------------------------------------------- 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
