Bruce, For mainframe we support Flashcopy, but for Open Systems we provide a common pool for Copy on Write (aka Snapshot).
Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of Bruce Black > Sent: Sunday, 19 February 2006 1:44 PM > To: [email protected] > Subject: Re: Disk vs Tape scenario > > Let me elaborate on what Ron said. > > There are essentially 3 technologies out there for "instant" replication > of data. > 1) Snapshot, in the IBM RVA and the StorageTek(Sun) disks, was truly > instant, since the architecture allowed data to be copied by just > copying pointers in memory. I won't go into all the gory details, but > essentially it created two pointers, so that two different tracks (on > the same or different disks) pointed to the same track image on the real > disks. If one of those two "tracks" was updated, its data was written > to a new location and its pointer updated, the other still pointed to > the unupdated data. > 2) constant mirroring, such as EMC Timefinder/Mirror BCV and Hitachi > ShadowImage, keep a continously updated mirror of a given disk volume. > When you want to create a point-in-time image of the volume, you 'split" > the mirror and it instantly becomes a copy. > 3) instant copy - like Flashcopy and EMC Snap, copy datasets and volumes > by establishing a background session, which takes only seconds. The > copy can be treated as if it was instantly completed, even though the > control unit is still copying data in the background. Updated tracks > are copied immediately, before the update is allowed, to preserve the > original content. Unupdated tracks may or may not be copied (an > option); if a track on the target is accessed and it has not been > copied, the track from the original disk is fetched. > > BTW, Hitachi ShadowImage has a version of (3) for full-vol only. They > support FlashCopy for dataset copies. > > -- > Bruce A. Black > Senior Software Developer for FDR > Innovation Data Processing 973-890-7300 > personal: [EMAIL PROTECTED] > sales info: [EMAIL PROTECTED] > tech support: [EMAIL PROTECTED] > web: www.innovationdp.fdr.com > > ---------------------------------------------------------------------- > 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
