Thanks for clearing that up Eric. The magic that was going on behind
unionfs was the part I wasn't clear on. That was a great explanation.
So the only files that end up in the sandbox folder from the unionfs are
the
ones that actually need to be modified? Ie: the reads come from production
but are written to sandbox?
-----Original Message-----
From: news [mailto:[email protected]] On Behalf Of Eric Shubert
Sent: Saturday, May 02, 2009 12:23 PM
To: [email protected]
Subject: Re: [qmailtoaster] About Unioned Sandbox
Phil Leinhauser wrote:
One of the developers may clean up my answer if I'm off a bit but I'll
try
to explain.
The sandbox is an isolated build of your entire current setup. It copies
your build into it and then runs the update scripts against this
"virtual"
build. If there are any errors, the only thing that is broken is the
sandbox, not the production build. Once all of the patches are applied
to
the sandbox build and there are no errors, it tells you the build was
clean.
Then it asks if you want to apply it to the production build. At that
point, when you say yes, it throws the built sandbox system "over the
wall"
into the production folders.
This process does 2 things, first, it safely builds the patches into the
virtual build without jeopardizing the production build. Second, it
makes
the downtime VERY short (Less than a minute) while it applies the sandbox
build into production. If you have a lot of patches to apply, the sandbox
build can take a while. Mine last night was pretty far out and I think I
had every QMT module patched, it took about 45 minutes to build and apply
the sandbox but only 45 seconds to copy into production. Thus my QMT was
only down for 45 seconds.
Very good, Phil.
The copy sandbox vs unionedfs sandbox is a huge improvement. In the
past,
it would actually COPY your entire QMT system into a sandbox folder.
Just
this, BEFORE applying the patches took over an hour. Now the unionedfs
does
some magic that I'm not fully clear on but they are links to the files
and
not copies of them so the sandbox build takes only a few minutes.
Let me see if I can explain this part a little better. There are 3 types
of sandboxes: Copied, Linked, and Unioned.
A Copied sandbox is a normal copy of most of the system files. This
takes a large amount of disk space, and quite a bit of time to create. A
Copied sandbox is the least preferable type, but it works under any
circumstance. It was the first type developed.
The Linked type of sandbox was developed to reduce disk space
requirements. It creates hard links (directory entries, sort of like
windoze shortcuts) to system files instead of making actual copies of
them. All toaster and rpm files are still copied though, as they
shouldn't be changed in the sandbox. While the Linked type is a big
improvement over a Copied sandbox as far as disk space is concerned,
creating it still takes quite a while, although it is a good deal faster
than a Copied sandbox.
The Unioned type of sandbox was later developed for qtp-newmodel by
Justice London. This is also known as an Overlay file system. It's the
same thing that's used by "Live" CD distros. In essence, the existing
file system is used as a base for all reads. Whenever a file is to be
changed, a copy of the existing file is automatically made to a separate
area, and the changes are made to the copy. New files are also added in
the separate area. The existing/primary file system is never modified.
The Unioned type of sandbox is preferred. It's by far the fastest, and
it uses a minimal amount of disk space. Since it uses a kernel module to
implement a new filesystem type (there are several which might be used
depending on your kernel version), the kernel module needs to be
compiled and installed the first time you use it, and whenever your
kernel version changes. This is all automated (thanks to Justice), but
it does take a minute or so to run (small price to pay). The only
drawback to the Unioned sandbox is that they only work with kernel
versions 2.6.9 or greater. If your toaster runs on an older kernel,
qtp-newmodel will not offer you the option of a Unioned sandbox.
Thanks for the question, Anil, and the answer, Phil. I'll use this to
update the qtp-newmodel web page.
-----Original Message-----
From: Anil Aliyan [mailto:[email protected]]
Sent: Saturday, May 02, 2009 9:27 AM
To: [email protected]
Subject: [qmailtoaster] About Unioned Sandbox
Hi,
I want to know bout Unioned Sandbox. What does actually a sandbox do?
When
we run qtp-sandbox script and it prompts for "Would you like a unioned
sanbox (quicker, smaller) [y]/n:" what difference does it actually
makes???
Regards,
Anil Aliyan
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