Slow resilvering with mirrored ZIL

[Mark Felder]

On Wed, 03 Jul 2013 09:40:34 -0500, Daniel Kalchev <daniel at digsys.bg>  
wrote:

>
> What is happening during resilver is reading from the other drives in  
> the vdev and writing to the new drive. You mention four drives so I  
> assume this is an raidz? Is it possible that the old drives and the  
> zpool vdev(s) are 512byte sector size and the new drive is 4k sector  
> size? If so, you might experience severe slowdown. The only way to fix  
> this situation is to recreate the zpool -- copy data out of the pool,  
> create the pool with 4k alignment for vdevs and copy data back.

This might be what he's experiencing -- I ran into this recently when I  
knowingly put a 4K drive into a server that used 512b sectors in the  
zpool. It was an emergency as we ran out of 512b 2TB spares. As soon as we  
got a proper spare I did replace the drive and performance went back to  
normal and the resilver was extremely fast too.