On 28 August 2014 13:26, Walters, Gene P <[email protected]> wrote:
We are getting a new DASD box and are looking at what configuration we want > for Linux. Right now, most of our disk is MOD-9. On the new box, we were > thinking about MOD-27's. Is there a disadvantage to using the larger > size? Are there any redbooks or papers that discuss this issue? > With ECKD you have at most one I/O active at a time per logical volume. Going to devices that hold 3 times more data reduces your I/O bandwidth by the same factor. But there's more that changes: you're getting a new DASD subsystem that might have more control unit cache, more non-volatile storage, faster back-end devices to deal with cache miss. And I expect you may not trade in at 3:1 but grow the total disk space for your guests. Depending on the workload, the reduced I/O bandwidth may not be a valid concern at all. In the right configuration, Parallel Access Volumes (PAV) could address some of those challenges if that is licensed with the new DASD. You're most welcome to send me some of your data to discuss your migration plans. Rob van der Heij http://velocitysoftware.com/ ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
