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Re: [Xen-users] File System Doubt

To: Scott Serr <serrs@xxxxxxxxxxxx>
Subject: Re: [Xen-users] File System Doubt
From: Christian Horn <chorn@xxxxxxxxxxxx>
Date: Sat, 22 Sep 2007 19:57:00 +0200
Cc: Tomasz Chmielewski <mangoo@xxxxxxxx>, Artur Baruchi <mail.baruchi@xxxxxxxxx>, Xen-users@xxxxxxxxxxxxxxxxxxx
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On Sat, Sep 22, 2007 at 11:41:18AM -0600, Scott Serr wrote:
> Here is a question...  whats the preferred fastest backend to store a 
> disk image on?  Or...
I made experiments putting the file belonging to a domU in a ramdisk,
doing file-benchmarks in the domU obviously also only happen in the
dom0-ram, guess not much could beat that.

> maybe the fastest Xen virtual drive is actually a raw partition or RAID 
> or logical volume management?
You should layer this a bit.
First: raid or not raid is a question of money/speed/how reliadble your
want your data to be stored.

Second and indepently: lvm vs. file-backend.
If its worth the hassle benchmark with your usecases yourself, from my
benchmarking ive seen filebased domU on internal disks have been faster
for i/o than ones on lvm.
On iscsi lvm did a bit better than filebased. Filesystem was xfs, and
the test was only raw writing in the domU. And just using the ancient
file: syntax for file-domU since SuSE just recently fixed the tap:aio

> filesystem on /dev/md0 and that is where my image files are.  I expected 
> that this would be quite fast, but my drives seem to sketch around 
> ALOT.  I can't imagine that LVM would buy you any more performance.  
> Would ext3?  
>From what i recall from filesystem-benchmarks with reiser you get a bit
better performance, especially when using many small files (which isnt
the case here) and at the cost of higher cpu-usage in dom0 here.


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