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Virtual Guest getting better hdparm results than host
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6thgenA34
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Joined: 05 Mar 2012
Posts: 22

PostPosted: Tue Mar 13, 2012 3:37 am    Post subject: Virtual Guest getting better hdparm results than host Reply with quote

I'm trying to study for the LPIC1 so I installed VirtualBox on my laptop. The thing is that I get better Timing buffered disk read running hdparm from with in the guest OS than the host OS. It's not much of a problem, I just wanted to find out the answer. It been puzzling me why this is happening. Used latest VirtualBox to make the guests.

Gentoo Kernel 3.2.1 Sata 1 + RAID 0 + ext4
hdparm -tT results
Timing cached reads = 1023.62 MB/sec avg
Timing buffered disk reads = 70.34 MB/sec avg

Guest OS Ubuntu kernel 2.6.24-26 ext3
hdparm -tT results
Timing cached reads = 960.57 MB/sec avg
Timing buffered disk read = 120.72 MB/sec avg

I was going to try to do software raid inside the guest OS too. But thought that would be over the top and not get any added performance.
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lyallp
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Joined: 15 Jul 2004
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Location: Adelaide/Australia

PostPosted: Tue Mar 13, 2012 3:43 am    Post subject: Reply with quote

Quite possibly it is the Host buffering that is affecting your timings.

After all, virtualbox is just another application to the host, with all the buffering, etc.
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Aquous
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Joined: 08 Jan 2011
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PostPosted: Tue Mar 13, 2012 7:38 am    Post subject: Reply with quote

VirtualBox doesn't properly honour sync requests sent by the virtual OS.
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6thgenA34
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Joined: 05 Mar 2012
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PostPosted: Wed Mar 14, 2012 3:55 am    Post subject: Reply with quote

Is there a way to properly benchmark within the virtual OS? Or just have to use a stop watch ?
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