Re: Poor disk performance in NetBSD DomU, again

["Michael L. Hitch" <mhitch%lightning.msu.montana.edu@localhost>]

On Sun, 11 May 2014, Yi Qiao wrote:

> So at this point I'm lost in terms of how to remedy the DomU write
> speed loss, since there is little to tinker with in the config file.
> I'm not ready to give NetBSD up just yet. I stopped running Linux
> since kernel 2.6.32, and every time I'm forced to run it, I feel dirty
> and obese. Any help would be greatly appreciated ;)

  You might try running 'iostat -d -x wd0 5' on the DOM0 (and the 
equivalent on the DOMU)  and compare the reads vs writes.  I experienced a 
similar problem when I tried using a disk image file on the DOM0, and I 
saw lots of reads on the disk as well as writes, while iostat on the DOMU 
was showing just writes.  I presumed that the DOM0 was doing 
read-modify-write operations which are quite slow.  If I remember 
correctly, using a disk image was done with vnd(4), so I could also run 
iostat on the vnd device.  I think you can also pass an LVM device to 
iostat, so you can see what it shows for reads and writes.

  I ended up using partitions on my DOM0 disk and was able to get 
reasonable write rates.  I would think that lvm should be similar, but 
it's been a while since I've done anything with lvm.  I think I was 
contemplating using lvm on the system where I ended up using disk 
partitions, but probably ran out of time to experiment.

Mike

---
Michael L. Hitch                        mhitch%montana.edu@localhost
Operations Consulting,  Information Technology Center
Montana State University, Bozeman, MT     USA