4drive RaidZ2 vs Mirrored vdev CPU and RAM requirements

[Cybernetika]

Hi.

I'm upgrading my current mix or 6 different sized mirrored drives for 4x 10TB drives.
As it's common with 4 drives I've ended up with the dilemma of choosing either RaidZ2 or mirrored vdevs.

Since I'm okay with redundancy that 2way mirror offers (It stores 2 PC backups and media served by plex) my main question boils down to whether mirrored pool is considerably easier on my hardware.

I'm running SCALE with 16GB of ECC memory, Scale reserves half of that for apps. That means I'm left with 8GB for ZFS. I'm also currently using very low power E3-1220L v3 (13w!) CPU. Although I have another more powerful and power hungry cpu to swap to if needed. But 16GB is my upper limit with current MB (server grade mini-ITX boards are expensive and hard to find)

Does anyone have reliable information about whether mirrored setup would be easier on my system resources considering I'm under recommended spec for this kind of HDD space on ZFS?

Show : Full system spec:

4x 10TB 7200rpm mix enterprise/nas drives
Silverstone DS380 modded (8bay hot-swap)
Asrockrack E3C226D2I
2x8GB DDR3-1600 ECC
Intel Xeon E3-1220L v3 (13w!) + Arctic 11 Alpine plus
Nvidia P600
Corsair SF450

2xNoctua NF-F12 PWM
1xNoctua NF-A12x25 PWM

 

[Arwen]

Writing for a 2 vDev, 2 way Mirror would be less overhead for small writes than a 4 disk RAID-Z2. You would even get more IOPS on a 2 x Mirror vDevs.

However, for larger writes, it may not make much difference.
Reads can be different. With a 4 disk RAID-Z2, you only have 2 data disks. But, in the 2 vDev 2 way Mirror, you have 4 data disks, well, sort of. If one set of the vDevs is reading, the other can also be reading, something entirely different. (They are Mirrors, with identical data...)

 

[ChrisRJ]

I'm also currently using very low power E3-1220L v3 (13w!) CPU. Although I have another more powerful and power hungry cpu to swap to if needed.

The "L" means lower TDP than a comparable CPU, but not lower power consumption overall. More than 10 years ago (before Sandy Bridge) there was a pretty good correlation between TDP and power consumption. But since then this difference is gone, except for running the CPU at full throttle all the time. So in a NAS setup the L version provides no measurable benefit to power consumption.