RFC: GEOM MULTIPATH Rewrite

[Mark Felder]

Hi all,

Building dual ZFS SANs at work with this hardware:

HP DL360 head units // 18GB RAM // Intel SSDs for zil/cache
LSI SAS 9201-16e
DataOn Storage DL-1630 with dual controllers filled with 2TB SATA 
Hitachis + LSI SAS transposers


I originally installed FreeBSD but my fight with gmultipath was not 
going well. I wasn't happy that it didn't have ACTIVE/ACTIVE and I also 
was discouraged by the ability to make it panic. I flirted briefly with 
OpenIndiana, but that whole platform needs to die as it's so painful to 
use. The weirdly horrible interactivity wasn't confidence-inspiring 
either -- why did it take 10 seconds to display "top"? Why were ZFS pool 
operations so slow? Very strange!

This morning I found you actually released gmultipath patches and I 
must say -- this works FANTASTIC now! I can be writing 500MB/s+ and pull 
the cables at random and it's nearly transparent in passive and active 
modes. I urge you to commit this so it gets more testing, but I will be 
putting FreeBSD9 + gmultipath in production soon. I just need to do some 
more benchmarks and I might switch the scheduler to 4BSD because this 
box will be doing nothing but I/O and network traffic and my research 
indicates ULE is not optimal in that type of a workload.


Cheers,


Mark