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

On Wed, 30 Jun 2010 07:54:55 +0200 (CEST)
Mikael Abrahamsson [off-list ref] wrote:

On Wed, 30 Jun 2010, Roman Mamedov wrote:

quoted

 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.

This is not necessary. See the dd man page about the conv=fdatasync switch.
You can even test with just 256 MB this way, and still get an extremely
accurate result.

Three consecutive runs with "count=256" on a machine with 4GB of RAM:
268435456 bytes (268 MB) copied, 4.76846 s, 56.3 MB/s
268435456 bytes (268 MB) copied, 4.79682 s, 56.0 MB/s
268435456 bytes (268 MB) copied, 4.79307 s, 56.0 MB/s

-- 
With respect,
Roman