it is my understanding for write (fast) consider faster HDD (SSD) for ZIL for read consider faster HDD(SSD) for L2ARC There were many discussion for V12N env raid1 is better than raidz
On 5/10/2011 3:31 PM, Don wrote:
I've been going through my iostat, zilstat, and other outputs all to no avail. None of my disks ever seem to show outrageous service times, the load on the box is never high, and if the darned thing is CPU bound- I'm not even sure where to look. "(traversing DDT blocks even if in memory, etc - and kernel times indeed are above 50%) as I'm zeroing "deleted" blocks inside the "internal" pool. This took several days already, but recovered lots of space in my main pool also..." When you say you are zeroing deleted blocks- how are you going about doing that? Despite claims to the contrary- I can understand ZFS needing some tuning. What I can't understand are the baffling differences in performance I see. For example- after deleting a large volume- suddenly my performance will skyrocket- then gradually degrade- but the question is why? I'm not running dedup. My disks seem to be largely idle. I have 8 3GHz cores that also seem to be idle. I seem to have enough memory. What is ZFS doing during this time? Everything I've read suggests one of two possible causes- too full, or bad hardware. Is there anything else that might be an issue here? Another ZFS factor I haven't taken into account? Space seems to be the biggest factor in my performance difference- more free space = more performance- but as my fullest disks are less than 70% full, and my emptiest disks are less than 10% full- I can't understand why space is an issue. I have a few hardware errors for one of my pool disks- but we're talking about a very small number of errors over a long period of time. I'm considering replacing this disk but the pool is so slow at times I'm loathe to slow it down further by doing a replace unless I can be more certain that is going to fix the problem.
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