Adam Thornton wrote:
Or diag250. Sure, doesn't work on the metal. Nevertheless.
Well.. Diag 250 is just a way to talk to a DASD. Whatever you do with Diag 250, you can also do with SSCH, an ORB and some CCWs... So even if Diag 250 isn't embedded in the kernel, you should still be able to IPL and mount your root FS. Now about Diag 250.. What's the gain ? performance ? let's face it.. CP has become very efficient at translating VM issued CCWs to real CCWs over the past 40 years or so.. When dealing with a 1.2 Mips 4341 Model 2, CP Assisted I/Os made sense.. now, With a 90,000+ MIPS z10.. well.. And if you're using Diag 250 so that you don't have to translate a block number to CCCCHHRR, you're just shifting the work from the Virtual Machine user mode to CP supervisor mode. Now.. Simplicity ? Device independence ? well, to support LPAR, you're going to have to deal with CCWs and device geometry anyway. XC I/O ? XC is 31 bit only ! (and we're all going 64 bit anyway !) - Besides, I don't think Linux understands XC. Basically, you now have to deal and maintain 2 methods instead of a single method to achieve the same result.. to me, it's more of a loss than a gain ! The *only* gain I see is being able to leverage CP I/O Error Recovery Procedures - and logging (which you get on minidisks.. anyway ! even if issuing I/O to Minidisks with SSCH). What I am saying here : Just like with initial ramdisks, It's not because something is 'possible' that you have to use it ! IMHO, Diag 250 makes sense in a CMS environment.. initrd makes sense on distributed systems.. and neither belong on Linux for z (except, as I stated before - in the case of initrd - for install & recovery). Of course, Adam (or anyone else), you are welcome (and encouraged) to prove me wrong :P --Ivan ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
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