Peter, ROTFL a cache miss will never take just 1ms. Seek and latency are still alive and well, so you are looking at 6-9ms for a read cache miss in a relatively idle system.
For read cache hit a of a 4KB block will be around 0.2-0.3 ms, again in an idle system. For a write hit the copy products in use can alter the response time significantly, from a few 100ths of ms for in system copy to several ms for synchronous remote copy. Again this assumes activity on a relatively idle machine. If you are using internal SATA drives, FlashDrives, or virtualized storage there will be an even greater range of rough figures to choose from. For the original OP's purposes I would suggest 0.5ms for cache hit and 9ms for cache miss would represent numbers for 4KB blocks in a generic storage system under load. Ron > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of > Hal Merritt > Sent: Wednesday, January 06, 2010 9:14 AM > To: [email protected] > Subject: Re: [IBM-MAIN] How long does an I/O take (very roughly)? > > Ignoring a lot and oversimplifying, I believe that modern DASD should > routinely deliver 0.1ms (hit) and 1ms (miss). > > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of > Hunkeler Peter (KIUP 4) > Sent: Wednesday, January 06, 2010 10:08 AM > To: [email protected] > Subject: How long does an I/O take (very roughly)? > > Hi, > I'm about to update a chart I'm using to illustrate the > relative speed of various actions like CP cycle, storage > access, etc. > > Does it still hold true that an I/O from controller cache (cache > hit) takes about 1ms and and I/O from the platter (cache miss) > takes about 5ms. All I want is two very rough figures. I don't > want to consider different hardware or attachement types. > > -- > Peter Hunkeler > CREDIT SUISSE AG > > > NOTICE: This electronic mail message and any files transmitted with it are > intended > exclusively for the individual or entity to which it is addressed. The > message, > together with any attachment, may contain confidential and/or privileged > information. > Any unauthorized review, use, printing, saving, copying, disclosure or > distribution > is strictly prohibited. If you have received this message in error, please > immediately advise the sender by reply email and delete all copies. > > ---------------------------------------------------------------------- > 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
