RAID question

fred974

fred974

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
 
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.
 
You can't use RAID-Z (or any other RAID-5 solution), it requires a minimum of three disks and you only have two.
 
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.
Click to expand...
That doesn't seem to be correct.

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

Code: 
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.
 
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.
 
fred974 said:
What is ZFS mirror performance like?
Click to expand...

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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