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Re: Poor disk performance in NetBSD DomU, again

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.


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

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