Re: [Xen-users] Optimizing I/O

["lists@xxxxxxxxxxxx" <lists@xxxxxxxxxxxx>]

>> The speed differences are instantly obvious when
>> connecting to a VM based server compared to stand alone.
>> 
> Again, you caught me by surprise here. The newbie vs experienced thing :)
> Seems like you're a seasoned VM users. In general, I'd say any I/O
> optimization you previously used on other virtualization platform or
> standalone boxes should also work on Xen. This includes noatime, which
> makes huge difference when you're mostly serving static content (since
> you didn't give the article link that recommends against it, all I can
> say for now is "noatime is good").

Yes, and now I've lost the URL, sorry about that. Basically, it talked about a 
guy doing tests and finding that with noatime, the data could become 
inconsistent and other things. So, in your experience, this has not been a 
problem?

The thing about optimizing I/O is that the guests are still really just data on 
Ethernet ports, no matter how you cut it. Whether I ran many instances of a web 
server or multiple separate guests, does it not always add up to more resources 
being used from the host? Just seems that you'd want to have stand alone 
servers working full bore on serving up web pages in a distributed manner 
rather than just taxing a host with guests and all the extras needed for 
similar redundancy. Guess I'll have to run some tests once I get everything 
together and see what happens.
 
> Regarding VM vs stand-alone, I'm not sure about your setup (were you
> still using vmware?), but in my experience when serving the same load,
> a VM server (with local storage) is comparable to stand alone machine
> with the same resource and load.

My win machines are on VMware but the reason I'm setting up xen is to move my 
linux servers over toe xen. I wasn't really thinking of web servers but it 
won't hurt to run some tests once I have the environment together.
 
> Now if we're talking about :
> - using shared storage, or
> - converting several stand alone boxes into one using VM without adding
> resource, Then yes, your point about "instantly obvious" is valid.

Well, shared storage on the host for the guests but the web servers would serve 
from network storage.

> Best machines to virtualize are those which aren't using resource
> close to 100%. By virtualizing them you increase utilization and
> reducing idle resource, thus saving money. I think that was the basic
> principle.

That's pretty much been my approach. The plan is to take all non I/O intensive 
servers that do a lot of idling and virtualize them. Why have the heat, the 
power, the drives wearing down, etc when virtualizing them is so very efficient 
for these.

Mike


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