On Sun, 21 May 2017 16:15:08 +0000, Jesse 1 Robinson wrote: >The first (maybe only) hardware I know of that claimed no wasted >space was STK Iceberg, which was touted as being so virtual that >an emulated 3390 track actually left no unused track bits. I never >worked with one, but I heard horror stories about *all* the data >getting wasted when the Iceberg lost its brains and couldn't find >anything. ;-(
I worked with an RVA, which was an IBM-branded Iceberg. It worked very well for us. IIRC, it allocated space on the disk for logical tracks in sectors, and would allocate the number of sectors required for the data on each track. The data on the track was compressed before allocating space for it. It used RAID 6 in the disk array, with two parity disks in each raid group, improving reliability of the back end. One consequence of the compression was that there was no update in place. When a track was updated, the entire updated track was written to a new location on disk, and the index for that track was updated to point to the new location. Flashcopy was achieved by copying the indexes to the data and incrementing the count of logical tracks represented by those sectors. There are still manuals for the RVA: https://m.ibm.com/https/publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/handheld/Connected/Shelves/CP6BKS03 -- Tom Marchant ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
