Physically, that's true -- ultimately there is only one physical I/O in progress. However, by splitting up the disks into a larger number of small chunks and presenting them to Linux in the virtual machine configuration, the Linux system sees the smaller minidisks as separate volumes, and thus schedules multiple I/Os to what it thinks is multple devices. CP coordinates all the actual disk I/O and everybody wins.
If you can, stripe the pieces across multiple physical voluems, but it's not as important. -- db David Boyes Sine Nomine Associates > -----Original Message----- > From: Linux on 390 Port [mailto:[EMAIL PROTECTED] Behalf Of > McKown, John > Sent: Wednesday, March 26, 2003 2:56 PM > To: [EMAIL PROTECTED] > Subject: Re: minidisk vs. dedicate > > > David, > One question/observation. Ignoring PAV on the ESS or > equivalent, there can > still be only one physical I/O going to a physical volume (as > seen by VM). > Therefore, when using the MDISK in this fashion, it is a good > idea to put > the different MDISKs on separate physical volumes. Is this > still true? I'm > not as familiar with VM I/O as I am with z/OS. But I think > this is still a > hardware restriction. > > > -- > John McKown > Senior Technical Specialist > UICI Insurance Center > Applications & Solutions Team > +1.817.255.3225 > > This message (including any attachments) contains > confidential information > intended for a specific individual and purpose, and its' content is > protected by law. If you are not the intended recipient, you > should delete > this message and are hereby notified that any disclosure, copying, or > distribution of this transmission, or taking any action based > on it, is > strictly prohibited. > > > -----Original Message----- > > From: David Boyes [mailto:[EMAIL PROTECTED] > > Sent: Wednesday, March 26, 2003 1:48 PM > > To: [EMAIL PROTECTED] > > Subject: Re: minidisk vs. dedicate > > > > > > Yeah, that's what I assumed. I'm suggesting breaking the > full volumes > > into several smaller parts (say 3 1000 cylinder chunks) and > > aggregating > > the smaller chunks with LVM. You end up with more effective > spindles, > > which allow more I/Os to be in flight at the same time for the same > > filesystem. Works really well, especially for databases with fairly > > random query patterns. > > > > -- db > > > > David Boyes > > Sine Nomine Associates > > > > > > > >
