Ed, There are two similar methods available. One is Copy On Write and the other is Instant Split. In both cases when the copy is created there is a set of pointers back to the original copy - the actual source data is not copied at that point.
Now you have two set of pointers directed to the same data, which is a bit like having two windows looking into the same room. You can start using the second copy immediately, while continuing to use the first copy. Creating the first set of pointers takes seconds. The minutes vendors usually talk about includes the procedures and automation required to prepare for the copy to be done. For Copy On Write the original data will be copied to a backing location if it is updated. This may be a shared pool of space or a dedicated backing volume. For Instant Split the data is copied under the covers after the split, and the storage updates the pointers when data moves from source to targets. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of Ed Gould > Sent: Sunday, 19 February 2006 10:34 AM > To: [email protected] > Subject: Re: Disk vs Tape scenario > > On Feb 18, 2006, at 8:05 PM, Ron and Jenny Hawkins wrote: > > > Radoslaw, > > > > I think the point is that for shops that use in system copies > > (Shadowimage, > > Flashcopy, Timefinder, etc) the time it takes to do the backup has > > nothing > > to do with the speed of tape. > > > > All of vendors offer instant copy capabilities that can be > > completed easily > > in less than a minute, no matter if you copy a GB or a TB. > > ---------------SNIP---------------- > > Ron, > > This has always bothered me. I will play beginner here. How can any > vendor copy a GB (or a TB) *INSTANTLY* there are laws of physics > here. A pipeline (even FICON or dark fiber) can only carry so much > traffic in an INSTANT. > > I can understand warmed over copy (as data is updated the updated > data is transmitted) . Is this what you mean? > > Even then (to me) its questionable if there is a GB being updated. > > Please educate me in what is apparently FTL technology that has been > invented. > > Ed > > ---------------------------------------------------------------------- > 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
