# RAID question



## fred974 (Sep 26, 2013)

Hello all,

My server hardware can only support RAID 0 and 1.. (I have 2 disks).

My question is: am I better off using the hardware RAID1 or to use the software RAID-Z from FreeBSD? Will a software RAID-Z affect the system performance by a lot?

Thank you all.

Fred


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## wblock@ (Sep 26, 2013)

ZFS RAID-Z won't reduce performance, they're actually quite fast.  But it is pretty much required to have at least 4G of RAM, preferably more.

Another option is gmirror(8): RAID1 - Mirroring.  That is also software RAID, but does not need additional RAM.  It does not provide the additional features of ZFS, though.

I would prefer either of these to using hardware RAID controllers.

There is also graid(8), which supports motherboard RAID hardware: Software RAID Devices.


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## fred974 (Sep 26, 2013)

Thank you @wblock@


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## SirDice (Sep 26, 2013)

You can't use RAID-Z (or any other RAID-5 solution), it requires a minimum of three disks and you only have two.


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## wblock@ (Sep 26, 2013)

Doh, I didn't even think of that.  Could use a ZFS mirror, though.


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## fred974 (Sep 26, 2013)

What is ZFS mirror performance like?


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## ShelLuser (Sep 26, 2013)

SirDice said:
			
		

> You can't use RAID-Z (or any other RAID-5 solution), it requires a minimum of three disks and you only have two.


That doesn't seem to be correct.

According to the zpool(8) manual page the minimum amount of disks is (quote:):


```
The minimum number of devices in a raidz group is one more than the number of parity
disks. The recommended number is between 3 and 9 to help increase performance.
```
And there is the raidz1 type which has a single parity, thus requiring 2 disks.

Note that I have no hands-on experience here, I'm solely basing this on the documentation.

*Edit*:

Actually I'm mistaken here, overlooking the fact that raidz (or raidz1) still refers to a RAID-5 based setup. Thus you'll always need 3 disks due to the way RAID-5 works.

I got confused because it didn't become clear to me that the parity disk should actually be counted separately.


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## SirDice (Sep 26, 2013)

It might be possible but you lose one disk to parity so you might as well mirror it. Mirroring probably performs a bit better than RAID-Z (or RAID-5) because there's no need to calculate and distribute the parity information.


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## kpa (Sep 26, 2013)

fred974 said:
			
		

> What is ZFS mirror performance like?



ZFS mirror usually outperforms RAIDZ in both read and write performance, the penalty is of course that with a mirror you use more disks to gain the same amount of storage.


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