Thoughts on replacing a low-budget HW Raid with ZFS?

[Ovidiu]

I've got a budget server with a Intel Xeon E3 1245v2 CPU and 2x2TB HDs 7200RPM with a HW Raid controller (devices are mirrored) and I think 512MB cache on the RAID controller. The server has 32GB RAM

Performance is good and the server is mostly idle and has plenty of resources. I have about 5 LXCs and 2 KVMs running.

I'm thinking about switching to an almost identical server with 32GB ECC RAM and was wondering how the performance would compare if I used a ZFS RAID1 instead of the HW Raid?

I can afford to let ARC use up to 8GB of the total RAM.

The reason for considering the switch is to take advantage of all the benefits of ZFS.

Any thoughts?

 

[LnxBil]

It will be slower, but I cannot give any real numbers.

You're moving all raid computations, caching, etc. from the RAID controller to your system, so you need CPU time and memory. For synchronous writes, the data will be written twice, so you have half the power as before for this kind of writes.

 

[Ovidiu]

I get the part about no real numbers, thanks.
CPU wise it will be fine, CPU is mostly idle right now.
Memory, well, my VMs amount to up to about 20GB so as I said I have about 8GB free for ARc and the rest is buffer.

I've looked a bit into synchronous writes found a few articles like this one, but I'm not sure how/where exactly synchronous writes would apply to this situation as the system is basically only handling the virtual disks of the VMs so are those written to synchrously?

 

[LnxBil]

ZFS implies in Proxmox, that the KVM vm has to be in 'write back' cache mode, so there should not be a lot of synchronous writes from the VM side, that's write.

What do you mean by "rest is buffer"? Have you still ext4 running? Normally, ZFS do not use "external" buffers like ext4. ARC is the ZFS buffer.

 

[Ovidiu]

nope, by buffer I meant: it is there if I need it, i.e. for another LXC or whatever else might need some more RAM