[dm-devel] dm-thin vs lvm performance

[Jagan Reddy]

Joe,
 I was running more tests to get more data.

 To answer your questions, I always use dd to write zeroes to ramdisk( you can also see this in the script I attached). So the ramdisk is allocated. I use

dd if=/dev/zero of=/dev/ram oflag=direct bs=512 count=`blockdev --getsize /dev/ram`

I get 9000+MB/s on allocated ramdisk using aio_stress. I was running the tests on same ramdisk. The performance doesn't change if i run thin test first and then raw test.

I modified the test to divide 4G ramdisk into 2 ramdisks. ( ramdisk1=2G ramdisk2=2G). Then I create tp lun on ramdisk1 and lvm lun on ramdisk2. 


Numbers I see 


ramdisk 10125 MB/s

ramdisk1 9690.55

ramdisk2 9548.89

unallocated tp lun 2257.67

fully allocated tp lun 5742.14

ramdisk 10288.2

ramdisk1 9721.8

ramdisk2 9415.25

Data not written lvm lun 9258.24

Data written lvm lun 9126.04

I have attached the script I use and the output. I wonder if  using 16 quad core processor and doing lot of of parallel operations is causing the issue to be reproduced.

Thanks,
Jagan.




________________________________
 From: Joe Thornber <thornber at redhat.com>
To: Jagan Reddy <gjmsreddy at yahoo.com> 
Cc: device-mapper development <dm-devel at redhat.com> 
Sent: Sunday, January 22, 2012 12:24 PM
Subject: Re: [dm-devel] dm-thin vs lvm performance
 
On Fri, Jan 20, 2012 at 01:06:08PM -0800, Jagan Reddy wrote:
> One interesting thing I notice is raw ramdisk has 9000+MB/s throughput in my tests and 5440MB/s throughput in your tests.

Yes, and if the ramdisk is unallocated the throughput tests on my machine also give ~9G/s throughput.  Can you please double check that it's allocated.  eg, are you running all the tests on the same ram disk?  If you run the thin test first and then the raw test does the raw performance change?

> I remember you mentioning that you are running tests in a VM with 4G
> memory, while I run the rests on a standalone server with 16
> quad-core processors and 12G or ram (out of that 12G, I carve out
> 4G ramdisk). Attached are the cpu and memory information. Could
> that be causing an issue?

Well memory performance will have an effect.  But I'd expect your
number to be consistent with mine.

- Joe
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