Re: Write-intent bitmap decreases or increase performance of RAID5?

[Shaochun Wang <scwang@ios.ac.cn>]

On Wed, Jun 30, 2010 at 07:54:55AM +0200, Mikael Abrahamsson wrote:
> On Wed, 30 Jun 2010, Roman Mamedov wrote:
> 
> >  dd if=/dev/zero of=zerofile bs=1M count=2048 conv=fdatasync,notrunc
> 
> To be a bit more sure about accurate measurement, make sure the amount of 
> data you're transferring is twice the amount of RAM in the machine, the 
> above is only 2 gigs of data.
As suggested, I did the test again and got the following result:

	-bash-4.1$ sudo dd if=/dev/zero of=test.dd bs=1M count=5000 conv=fdatasync,notrunc
	Password:
	5000+0 records in
	5000+0 records out
	5242880000 bytes (5.2 GB) copied, 63.497 s, 82.6 MB/s

	-bash-4.1$ sudo dd if=/dev/zero of=test.dd bs=1M count=5000 conv=fdatasync,notrunc
	5000+0 records in
	5000+0 records out
	5242880000 bytes (5.2 GB) copied, 18.1033 s, 290 MB/s
	
I don't know why the second dd becomes 290MB/s and the first 82.6MB/s.

-- 
Shaochun Wang(王绍春) <scwang@ios.ac.cn>
State Key Laboratory of Computer Science,
Institute of Software,
Chinese Academy of Sciences
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