3x read to write ratio on dump/restore

[Daan Vreeken [PA4DAN]]

Hi Warner,

On Friday 09 January 2009 17:50:27 M. Warner Losh wrote:
> I just copied a disk using dump + restore.  I noticed something
> through the whole run of this 500GB operation:
>
>  L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w   %busy Name
>     3    231    231  14754    9.5      0      0    0.0   97.5| da1s1a
>     0     39      0      0    0.0     39   4982   10.0   38.7| da2s1a
>
> The read kBps was 3x the write kBps.  While the dump is going through
> the raw device, and the restore is going through the file system, I
> can't imagine why we'd have such a huge difference that would be utter
> consistent for the whole 15 hour run.
>
> Any ideas what gives?  I observed this with 16MB cache and with 32MB
> cache, fwiw.

I've noticed this too. Last week I upgraded a laptop harddisk and used dump + 
restore to copy files from the original harddisk (attached to the laptop 
using a USB bracket).
During the entire copy process I also saw about a 3x difference.


-- 
Daan