[Linux-PowerEdge] Extremely poor performance with LVM vs. RAW disc

Dan Pritts danno at umich.edu
Mon Nov 5 09:00:51 CST 2012

> If you want to test disk speed -- you should pre-allocate the file as 
> contiguous (you can
> do this on xfs... dunnow about ext4)....then when you 'dd', use direct 
> I/O -- and use
> nocreat,notrunc options on 'dd', so you are reading/writing to the 
> same area and aren't
> exercising the file-system's ability to allocate space, nor the OS's 
> buffer system.

Or, just dd to and from a raw partition.
Dan Pritts
ICPSRComputing & Network Services
University of Michigan

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