I pretty much disagree. Tools are there, lots of storage savings possible.
One system I
look at, i expect to save over 1/2 GB of REAL storage with xip implementation.
machines
do not need to be identical, it just takes an understanding of how to
implement, what to
include and specifically how to measure it.
David Boyes wrote:
I was wondering how many people are using DCSS to share code under
Linux? At this time we are looking at about 12 to 15 Linux guest
divided across two lpars. It is my understanding the Linux guest will
be running WebSphere and Oracle. I have found some information on
setting up the environment. The doc talks about performance gains and
memory savings that has some people here interested in looking at
DCSS.
Unless you have a larger number of *exactly* identical guests (>50 would
be my starting point to look at this) delivering the same function
within the same VM system with R/W data stored in other virtual machines
(ie, remote databases), it's probably not worth it.
What I've observed so far with DCSS-based filesystems is at best it
gives you some I/O avoidance (and correspondingly, some reduction in
caching bloat) on the executable portions of the applications. You'll
still see the virtual machines bloat up to their maximum defined size;
it'll just take longer for the kernel to dirty up the "spare" memory
with data pages.
Given the current state of the DCSS and XIPFS tooling, it's difficult to
manage systems that use the DCSS/XIP function, and you need to install
the applications in ways to rigidly separate R/O and R/W code and data.
This is not trivial to accomplish, especially with the two applications
you mention (it can be done, but it requires major surgery and an
intimate knowledge of what the apps puts where and what it is actually
up to during runtime).
Also, most of the memory bloat in those two applications is in private
R/W memory structures, which won't really benefit at all from the DCSS.
Both DCSS and XIP functions are interesting ideas, but until the tooling
gets more sophisticated, they're probably not going to see much use.
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note:If you can't measure it, I'm just not interested
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