As Radoslaw points out, there are a lot of things to consider. Personally, I count the number of bytes transferred at the program level and divide by the time to get the rate.
A real 3390 (do they still exist?) even reading just a R0 from a track will take as long as reading two 27K blocks of data from a track. A similar problem exists with a 32K blocksize on a 3390. The reason for this is you just have to wait for the disk to spin. Years ago we used to calculate how many times the disk had to spin, then determine how long that should take and see how close our elapsed actually was to that calculated ideal time. With an emulated 3390, I suspect the transfer rate is probably more consistent between the two 27K blocks vs 32K blocks. Chris Blaicher Senior Software Engineer, Software Services Syncsort Incorporated 50 Tice Boulevard, Woodcliff Lake, NJ 07677 P: 201-930-8260 | M: 512-627-3803 E: [email protected] www.syncsort.com Check out our Knowledge Base at www.syncsort.com/support Syncsort aims for the best product and service experience. We welcome your feedback. -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Bill Fairchild Sent: Tuesday, March 20, 2012 5:12 PM To: MVS List Server 1 Subject: megabytes per second New thread. What exactly does "MB/second mean when referring to how much data can be copied from a DASD to a tape? To be more precise, I am not interested in big MB vs. little mib, just the philosophy. Suppose I have a huge file on a "3390" virtual thing and I can copy whole tracks to tape at the rate of 100 MB/sec. Assume the tracks hold 50,000 bytes instead of 56,664 to make the math easier. Does 100 MB/sec. mean that I am copying 2,000 tracks per second? Maybe. What if there is nothing written on the tracks, but I don't know that until I read them in and then write the contents? Of course, there is always at least an R0 on every track, so they are not completely empty. If all they have written on them is R0, am I still transferring data at the rate of 100MB/sec? If each track were half full, would my effective data transfer rate be only 50 MB/sec? Bill Fairchild ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
