I'm pretty sure the ZIL is not mirrored. If it were, it wouldn't increase performance since you'd still have to wait for the disks to fsync their copy to guaran

I'm pretty sure the ZIL is not mirrored. If it were, it wouldn't increase performance since you'd still have to wait for the disks to fsync their copy to guarantee reliability. This is why Sun Storage products (and Nexenta, or homegrown clusters) put the ZIL SSDs in the JBODs and not the storage heads. You could of-course create a pool that did use a disk as the ZIL, but again, there'd be no point since the mirror has to be kept consistent otherwise it's worthless. Since the cache (L2ARC) is just cache, and you can lose it at anytime without data-loss, it is in the heads. Nit-picking. To be clear, the ZIL can (and should be) mirrored, you just want to do it with SSDs consistently. Mixing devices is possible, but you'll be limited to the performance of the slowest device. You can also create storage clusters with multiple heads. Again, a good idea IMO, but the ZIL is a critical component of the FS. If you lose it, you lose the whole pool (as a rule I think, but there might be clever hacks around that under special circumstances if you're lucky). So if you're going to multi-home your zpool, make sure the ZILs are in the shared-storage region. It's no good having redundant controllers if your ZIL is on the dead one.