fewer bigger disks vs more smaller disks

[ragametal]

This might already be answered but i couldn't find a post addressing this question directly.

I want to re-build my home server and re-use some of the drives i already own. My server currently uses Ubuntu but i want to go the TrueNAS route.

I have two options for my main data pool
1- use two 12 TB drives in a mirror configuration OR
2- use four 4 TB drives in a RAIDZ1 configuration.

Both would give me the same raw storage capacity of 12 TB and both would give me protection against hardware failure up to 1 disk.
Which would be the better choice?

With fewer disks i get a more simplified setup, reduce power consumption and i have more free space in my case to install disks in the future. However, my understanding is that re-silvering could take weeks which could stress the remaining disk to the point of failure. In which case all the data in the pool would be losts.

With more disks i don't have to worry about the resilvering time so much, the disks are less expensive and my understanding is that TrueNAS has better performance with more disks. This option is more complex, increases power consumption and leaves less space in the case for future upgrades.

 

[sretalla]

With fewer disks i get a more simplified setup, reduce power consumption and i have more free space in my case to install disks in the future. However, my understanding is that re-silvering could take weeks which could stress the remaining disk to the point of failure. In which case all the data in the pool would be losts.

You're mixing the downside of RAIDZ1 with the upsides of Mirrors.

The resilvering process for mirrors is far better than for RAIDZ1 and will not put excessive pressure on the remaining disk.

Overall, it seems mirrors would be better for you.

You will run at lower power with approximately the same IOPS and maybe only slightly lower throughput speeds as with RAIDZ1, but you will be able to expand the pool in future easily by adding 2 disks at a time, compared to needing 3 more disks to expand RAIDZ1 (with an additional VDEV).

 

[ragametal]

The resilvering process for mirrors is far better than for RAIDZ1 and will not put excessive pressure on the remaining disk.

I was indeed confused. Thanks for the clarification.
Based on this, it seems that there are no cons in my case with using two 12 TB disks in a mirror configuration.

 

[sretalla]

As I identified, perhaps a minor con will be in throughput (particularly the copy of very large files), where you may be able to get 20% or so more MB/s in read operations on RAIDZ1, but generally it won't be different or maybe even better when dealing with large copies of small files (which are IOPS heavy).

It will certainly be better for VMs if you're going to run any of those.

 

[ragametal]

I'm more than OK with that performance toll. This server will be mostly for static data (media, backups, etc,) so performance is not necessarily a priority.

I have no plans to run VMs but I may run some services in Jails or containers (if i go with scale).

 

[Davvo]

More disks = more chance of failure.
More vdevs = (way) more chance of failure.
Bigger disks = longer resilver time (more chance of failure).
Disks want to kill your data.

A 8-wide RAIDZ2 vdev is safer than 4 vdevs each in 2-way mirror configuration.
If you are interested, play with this tool.

R2-C2

jro.io

 

[ragametal]

More disks = more chance of failure.
...
Bigger disks = longer resilver time (more chance of failure).

That is exactly why i was asking this question.
Thanks for the R2-C2 resource, it ended up confirming that a mirror configuration is less likely to loose data than a 4-disks vdev in radz1 configuration.

The only thing that tool does not take in consideration is the long re-silver time associated with bigger disks. However, as @sretalla said, the resilver time is lower in a mirror vdev than in a raidz1 vdev. Therefore that is less of a concern.

All in all everything indicates that in my case a mirror vdev with 2 big disks will serve me better than a vdev with 4 smaller disks in raidz1 configuration.

Thanks for the responses and help.

 

[Davvo]

If you want to explore deeper the following resource might interest you.

ZFS Storage Pool Layout

This resource was originally created by user: @Davvo on the TrueNAS Community Forums Archive. https://www.truenas.com/community/resources/zfs-storage-pool-layout.201/download [1] This amazing document, created by iXsystems in February 2022 as a “White Paper”, cleanly explains how to qualify...

www.truenas.com