On Mon, Feb 08, 2010 at 04:58:38AM +0100, Felix Buenemann wrote: > I have some questions about the choice of SSDs to use for ZIL and L2ARC.
I have one answer. The other questions are mostly related to your raid controller, which I can't answer directly. > - Is it safe to run the L2ARC without battery backup with write cache > enabled? Yes, it's just a cache, errors will be detected and re-fetched from the pool. Also, it is volatile-at-reboot (starts cold) at present anyway, so preventing data loss at power off is not worth spending any money or time over. > - Does it make sense to use HW RAID10 on the storage controller or would > I get better performance out of JBOD + ZFS RAIDZ2? A more comparable alternative would be using the controller in jbod mode and a pool of zfs mirror vdevs. I'd expect that gives similar performance to the controller's mirroring (unless higher pci bus usage is a bottleneck) but gives you the benefits of zfs healing on disk errors. Performance of RaidZ/5 vs mirrors is a much more workload-sensitive question, regardless of the additional implementation-specific wrinkles of either kind. Your emphasis on lots of slog and l2arc suggests performance is a priority. Whether all this kit is enough to hide the IOPS penalty of raidz/5, or whether you need it even to make mirrors perform adequately, you'll have to decide yourself. -- Dan.
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