On Thu, May 20, 2010 at 3:39 PM, Billy Bingham
<[email protected]> wrote:
> Hello all,
> Risking the old saying that it's better to have people think you're stupid
> than to open your mouth and remove all doubt :)
> If VM is doing I/O to one DASD volume only, say a DDR DUMP or RESTORE, and
> everything else is equal, will VM use multiple channels to get to the one
> volume, or will it do all it's I/O on whatever channel it gets first and
> only that one channel?
DDR will wait for an I/O to complete before it starts the next one.
And with all I/O to the same real volume, it would also be serialized
by z/VM. So if nothing else is going on z/VM can do with just one
channel. I don't think CP will try to balance over the channels, but
picks another one when the first choice is busy. Some DASD
configurations encourage CP to prefer one channel over the other.
In your scenario, you would see it all go via one channel. Something
like this (with apologies for those who read mail in proportional
font):
ESACHAN Velocity Software-Test VSIVM4 ESAMON 3.7
Channel Performance Analysis CHANNEL 00
Pct Channel <--------------Data
<Channel> Utilization <---Reads/Second-->
CHP Shr Class Typ LPAR Total LPAR TOTAL Pct Max
--- --- ----- --- ----- ----- ---- ----- --- ----
00 Yes FICON FC 0.1 0.1 4 6 0 195K
01 Yes FICON FC 5.8 5.8 6405 6416 3 195K
I can't really think of real life situations where that would be a concern.
Rob
--
Rob van der Heij
Velocity Software
http://www.velocitysoftware.com/
