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Raidz2 - 5 or 6 disks?

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fatality88

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Jul 2, 2011
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I am currently running a ESXi/ZFS all in one box with Solaris 11 Express and napp-it with 4GB assigned to it.
I currently have 4xHitachi 7K3000 3TB drives in a raidz config.
I am looking to increase redundancy with raidz2 and lower power consumption with some 5K3000 3TB drives.
Originally, I was going to go with 5x5K3000 drives with raidz2 but I am reading that 6 drives is an optimal amount for raidz2.
However, with 6 drives, I've calculated I'm going to have the same power consumption as the original 4x7K3000.
What is the benefits of having the 6 drives in raidz2? I'm not in need of the extra storage, that would be a bonus, but would rather conserve the power.
Also, would 4GB be enough for raidz2 (5 or 6 drives)?
Any suggestions would be appreciated! :)
 
In general, you get a (small) performance increase if the number of "data" drives is a power of 2. For raidz2, that would be 6 drives (4+2), correct. Here's a thought: give up one drive worth and go with a raid10 config (3 2-drive mirrors.) This will really improve random reads drastically - this can help a lot if you have several VMs, since ESXi will be doing lots of random reads. Also, 4GB ram is fine (has nothing to do with raidz2 per se.) Pretty much, ZFS can use any ram you throw at it - if you have a smaller amount, your read cache will be smaller, and you will need to go to disk more often. My all in one has 8 VMs running (fairly light usage), with a 3x2 raid10 mirror (WD blue drives.) I have 6GB assigned to the SAN VM, 5GB of which is used for the ARC (read cache.) I am hitting about 80% in the cache...
 
Thanks for the reply. :)
Sorry, I forgot to mention, I will be using 2 SSD's mirrored for my VMs. The raidz2 array will be strictly data so performance isn't a priority as such (more redundancy and power consumption)...
 
The performance difference isn't very big. I wouldn't worry about it.
 
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