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[Xen-users] Xen Sparse Image Files and MaxIQ SSD

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Subject: [Xen-users] Xen Sparse Image Files and MaxIQ SSD
From: Andy Pace <APace@xxxxxxxxxxxxx>
Date: Thu, 8 Jul 2010 16:08:35 -0500
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Thread-topic: Xen Sparse Image Files and MaxIQ SSD

Hello list!


I’m currently storing Xen sparse image files for VM’s on remote attached storage devices, and looking to increase the amount of IO available on it. I’ve ran across MaxIQ SSD read acceleration caching, and was wondering if this is a smart move, given the way we use the sparse image files.


My fear is that the MaxIQ will cache entire image files, instead of  the most commonly accessed files *INSIDE* the VM. Can anyone confirm or deny my theory?


I’ve talked with Adaptec and this is what they told me:



It's hard to say exactly. Keep in mind that a RAID card isn't aware of files, only blocks. So depending on how the blocks are accessed, the MaxIQ product may or may not help you. My first impression with 30GB files is that it may not be very helpful.



So, that being said, right now we are accessing the image files using the ‘file’ mode:


    <disk type='file' device='disk'>

      <driver name='file'/>

      <source file='/distributed/vms/29609/disk.img'/>

      <target dev='xvda' bus='xen'/>



Will the MaxIQ work in the way I want it to, or will I have to change the way we access the images? Or will it end up trying to cache entire images onto the SSD? Has anyone had experience with this type of application?

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