So ive been doing a lot of research on NAS and plan on going with freenas for my build. Most questions i've been able to answer with research, but I wasnt sure about this one on hard drive configuration.
lets say for simplicity that 2TB drives are 100$ and 4TB drives are 175$ and that I have 6 sata ports. You would think its most cost effective to go with the 4TB drives for pure TB/$. But from what I understand about raidz2, this is not the case.
6x2TB = 600$ for 12TB. In raidz2: 8TB available. 75$/available TB
4x4TB = 700$ for 16TB. In raidz2: 8TB available. 87.5$/available TB
You can see that the 4TB drives are actually less cost effective in this configuration.
Other considerations:
A 4 drives in z2 performs worse than 6 (not that i am overly concerned with speed), according to this research: https://calomel.org/zfs_raid_speed_capacity.html
You could say the advantage of going with 4x4 is that you could add 2 more drives eventually. But two drives would most likely be added mirrored(if you are concerned about safety), and this would actually reduce the safety of your z2 data if added to the pool, which i don't want to do. It would require another pool which is not that attractive.
Another disadvantage of 4x4 is if you do lose a drive, replacing 4TB drives is more expensive than a 2tb drive.
The only real advantage I see to a 4x4 config is the simplicity of having less drives, more chassis/board and powersupply options. And I guess if you dont want to run z2, you have more space.
My conclusions seem to go against common wisdom of the freenas forums, am i missing something here?
tl/dr
2tb drives seem more cost effective(among other reasons) for z2 pool than 4tb drives, even when 4tb drives are significantly discounted.
lets say for simplicity that 2TB drives are 100$ and 4TB drives are 175$ and that I have 6 sata ports. You would think its most cost effective to go with the 4TB drives for pure TB/$. But from what I understand about raidz2, this is not the case.
6x2TB = 600$ for 12TB. In raidz2: 8TB available. 75$/available TB
4x4TB = 700$ for 16TB. In raidz2: 8TB available. 87.5$/available TB
You can see that the 4TB drives are actually less cost effective in this configuration.
Other considerations:
A 4 drives in z2 performs worse than 6 (not that i am overly concerned with speed), according to this research: https://calomel.org/zfs_raid_speed_capacity.html
You could say the advantage of going with 4x4 is that you could add 2 more drives eventually. But two drives would most likely be added mirrored(if you are concerned about safety), and this would actually reduce the safety of your z2 data if added to the pool, which i don't want to do. It would require another pool which is not that attractive.
Another disadvantage of 4x4 is if you do lose a drive, replacing 4TB drives is more expensive than a 2tb drive.
The only real advantage I see to a 4x4 config is the simplicity of having less drives, more chassis/board and powersupply options. And I guess if you dont want to run z2, you have more space.
My conclusions seem to go against common wisdom of the freenas forums, am i missing something here?
tl/dr
2tb drives seem more cost effective(among other reasons) for z2 pool than 4tb drives, even when 4tb drives are significantly discounted.
