Thanks for the education. Chris
-----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Ron Hawkins Sent: Monday, August 18, 2008 3:55 PM To: IBM-MAIN@BAMA.UA.EDU Subject: Re: Here we go again (was z/OS Hot Topics 19) Chris, Yes there can be many concurrent IO transfers occurring to and from Cache. I actually find high Q-depth numbers, and ALIAS for that matter, become more important for cache miss IO. Cache miss is magnitudes longer than a cache hit and will quickly starve the Volume of PAV, or the LCU of HyperPAV, so that concurrent IO transfer will stall and UCB queuing will occur. Low cache hits require more alias than high cache hit. Disk drives can support processing a seek for read while concurrently writing into the SCSI buffer - sorta like two IO at once but not all the time. TID is the Target ID, and is analogous to the Device Address. HBA is the Host Bus Adapter and could be considered a channel. The Queue referred to in Queue depth can also process IO out of order based on ordering schemes and priority. The default queue for disks was to process the IO in 1st to last track order, but nowadays disk drives use a travelling salesman technique (think DFSORT Blockset) to sort the queue and reduce seeking. At one stage not all Array vendors enabled this queue management on the disk drives (I don't know about current models). Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On > Behalf Of Blaicher, Chris > Sent: Monday, August 18, 2008 12:40 PM > To: IBM-MAIN@BAMA.UA.EDU > Subject: Re: [IBM-MAIN] Here we go again (was z/OS Hot Topics 19) > > Ron, > > Education time for me- > > Given a queue depth of 8, do they have 8 actually doing data transfer > concurrently? Given the right configuration a PAV device can get a > BUNCH of I/O's doing concurrent data transfers from the same device. > > What is a HBA and a TID? LUN, I assume, is a Logical UNit. > > Just trying to broaden my understanding. > > Chris > ---------------------------------------------------------------------- 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
