Fragmentation fail - ZFS and a single SSD Hyper-V and FBSD 10.1

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gigatexal

I'm here to learn
Nov 25, 2012
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Portland, Oregon
alexandarnarayan.com
I'm passing through a single whole disk not the 1015 controller to a hyper-v VM running FBSD 10.1 and zfs ver 5000.

writing just zeroes with dd of about 10GB to the zfs volume (created on the passed through ssd) I get about 5% fragmentation after the first pass.

The first write is at 530MB/s with a clean and "cold" system, nothing written to the disk, nothing cached.

The second write is about 460 MB/s, same dd command just to a new filename.
fragmentation at the start is about 5%

The third drops to 360MB/s or so.
when the drive is about 70 or so percent full fragmentation hits > 80%.

Any thoughts on why performance is dying so badly? I know it has to do with fragmentation but I am not sure why it fragments so quickly.

I'm going to try passing the whole controller to the vm and see what happens.
 
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