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Re: [Xen-users] File System Doubt

To: Artur Baruchi <mail.baruchi@xxxxxxxxx>
Subject: Re: [Xen-users] File System Doubt
From: Tomasz Chmielewski <mangoo@xxxxxxxx>
Date: Sat, 22 Sep 2007 18:58:33 +0200
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Artur Baruchi schrieb:

Is there any difference in using a file as disk or a big partition to Xen?
Im running some benchmarks and Xen shows a great performance while
creating and removing files, I mean, a performance much better than a
real machine...
So im figure out that the fact that im using a simple file as disk to
Xen is the reason of this great performance... Can this guess be true?

I guess it can be true, if the tests were short.

dom0 treats this "file image" as a regular file, so, as you write to it from domU (create/remove files), dom0's kernel may decide not to actually "sync" the file yet. That is, your changes are purely in RAM at this point, and this is why it's so fast. Now, try to press reset button in dom0, and after reboot, see how many files you really have - or, if you can still open the image ;)

"Creating and removing files" is not that great benchmark.

Try it with a bigger amount of files (millions etc.), I expect the performance won't be better for an "image file" partition anymore.

Tomasz Chmielewski

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