On Tue, Dec 13, 2005 at 11:19:23AM +0100, Carsten Otte wrote:
I second your thoughts regarding block vs track caching,
but I doubt that a scenario exists where MDC for non-shared
mdisks outperforms reasonable distribution of the available
storage to the linux images. Would you care to show
Barton Robinson wrote:
I think I have a different perspective.
Storage is a valueable resource. Caching takes storage. You
have a choice of where to cache, your xx number of linux
servers could all be big enough to cache. That is inherantly
bad. Sizing of linux virtual machines is meant to
James Melin wrote:
My VM guy here is saying that he read some place that having mini-disk
cache turned on for mini-disk volumes used by linux for system disk is a
good thing.
I have'nt seen a measurement where MDC is not counter-productive for mdisks
that are not shared between different Linux
Jim,
If you don't want to turn it off , you may want to limit the amount of
storage that is used for minidisk cache.
You can do this by using the following commands .
cp set mdcache storage 0M 2M(this would limit central mdcache to 2M)
cp set mdcache xstor 0M 2M (this would limit
Changing the subject
What is the size of MDC in your shop?
I guess to make the numbers mean something, please include:
1. Processor (number of processors, MIPS) under VM's control
2. Real memory size
3. About of dasd
On my old MP3000 with 1GB, I set MDC to a fixed 100MB. Even at the end
Just an example and not a bad one. My next sentence said .
What limits should you use?
That you will have to play with to see what is best for your environment.
John
Changing the subject
What is the size of MDC in your shop?
I guess to make the numbers mean something,
!)
Mark Post
-Original Message-
From: Linux on 390 Port [mailto:[EMAIL PROTECTED] Behalf Of
Carsten Otte
Sent: Monday, December 12, 2005 3:36 AM
To: LINUX-390@VM.MARIST.EDU
Subject: Re: VM Mdisk cache and Linux disk caching
James Melin wrote:
My VM guy here is saying that he read some
Mark Post wrote:
So, if we take out the double negatives, did you mean to say:
Every measurement of MDC I have seen was counter-productive if the mdisks
were not shared between different Linux images within a VM. ?
(Just trying to verify my understanding, not criticize your writing ability
I think I have a different perspective.
Storage is a valueable resource. Caching takes storage. You
have a choice of where to cache, your xx number of linux
servers could all be big enough to cache. That is inherantly
bad. Sizing of linux virtual machines is meant to reduce the
cache size
James Melin [EMAIL PROTECTED] wrote:
My VM guy here is saying that he read some place that having mini-disk
cache turned on for mini-disk volumes used by linux for system disk is a
good thing.
My position has always been that Linux is caching what VM is caching and
it's a double fault. Since I'm
After thinking about it a little more since my reply on Friday...
If you have a good performance monitor that can measure the MDC hit rate
on your Linux packs (note I said hit rate, not hit ratio), if MDC has a
high hit rate, then MDC is working well for that pack. If it has a low
hit rate,
On 12/9/05, James Melin [EMAIL PROTECTED] wrote:
My VM guy here is saying that he read some place that having mini-disk
cache turned on for mini-disk volumes used by linux for system disk is a
good thing.
With current z/VM releases there are certainly cases where you have
benefit of MDC for
My VM guy here is saying that he read some place that having mini-disk
cache turned on for mini-disk volumes used by linux for system disk is a
good thing.
My position has always been that Linux is caching what VM is caching and
it's a double fault. Since I'm not the VM guru (and neither is he
It seems to be one of the topics that don't have an easy answer.
On one side, the best cache is the cache that is the closest to the
action. Oracle SGA cache is better then the Linux cache. Linux cache
is better than MDC cache. MDC cache is better than DASD controller
cache. That is when all
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