Should I ditch my mirror?

[Naesstrom]

This is just a quick question I hope. I've been using freenas for what feels like ages and when I started out I made my volume a mirrored one for safety and basically that was what I recognised so now it looks like this:

Each disk is 4Tb each but I've now bought a new CPU, case, etc and two 6TB disks... Before I just expand my current volume I wanted to see what you recommend. I've been trying to read the documentation etc, and a bunch of forum posts but it might be that it's not my native language, I just don't get it!

The server is primarily used for plex/CB/SR and as a secondary backup for my photos (main backup is google) so I don't feel that redundancy is all that important anymore. What do you suggest? create a new volume and follow the guide here and migrate the data?

 

[nojohnny101]

Seeing as raidz1 is not recommended anymore, seems like a 6 disk raidz2 setup would be best. Most on here say 6 disks is the sweet spot for raidz2.

Good balance of performance and fault tolerance.

 

[BigDave]

I don't feel that redundancy is all that important anymore.

Do you have plans for the original four drives currently in your pool? If the answer is yes, then your reasoning seems sound.
That is, of course, assuming you are making the two new 6TB drives a simple mirror.

 

[Naesstrom]

Seeing as raidz1 is not recommended anymore, seems like a 6 disk raidz2 setup would be best. Most on here say 6 disks is the sweet spot for raidz2.
Good balance of performance and fault tolerance.

Yeah that was what I was thinking to, and that guide to transfer to a new volume didn't see to complicated :D

Do you have plans for the original four drives currently in your pool? If the answer is yes, then your reasoning seems sound.
That is, of course, assuming you are making the two new 6TB drives a simple mirror.

My plan was to use all 6 drives and being able to use more of the space then 50% :D

 

[BigDave]

My plan was to use all 6 drives and being able to use more of the space then 50%

At this point in order to use all 6 drives in a RAIDz2 volume, you will have to destroy your pool and re-configure it.
Do you have other space to copy your data to?

 

[BigDave]

If you can get the data copied off the current pool, you could build a 6 drive RAIDz2 volume
which would use only 4TB of the 6TB drives. You can figure your usable space with this:
Biduleohm's RAID calculator
You will use the 4TB choice as FreeNAS will force all drive capacity down to the smallest
drive used, in your case 4TB.

 

[Naesstrom]

Hmm, that doesn't sound so good. Looking at the calculator you linked there doesn't seem to be any improvement in available space with a raidz2 compared to the mirrored one.

Sent from my Nexus 6P using Tapatalk

 

[gpsguy]

With 4 just drives, that's correct. The difference is that you can loose ANY two drives. With striped mirrors, if you loose 2 drives in the same 2 drive mirror, you lose the entire volume.

Looking at the calculator you linked there doesn't seem to be any improvement in available space with a raidz2 compared to the mirrored one.

 

[BigDave]

If my quick and dirty calculations are correct (caution, my math SUCKS)...
Your net gain (by tearing down your mirrors) by going with a 6 drive RAIDz2 would be a paltry 1.6TB,
over the option of adding the two 6TB drives as a mirrored Vdev to your current volume configuration.
But as @gpsguy said, you gain big with the RAIDz2 configuration when it comes to possible data loss.

Also, if you go with the RAIDz2 AND in the future you replaced the remaining four 4TB drives to 6TB,
upon replacing the last 4TB drive with a 6TB drive, your pool would automagically expand to 36TB MINUS
overhead, redundancy, swap space (oh for god's sake, use the calculator)!

 

[gpsguy]

The OP just needs to read your signature.

"If you start with 4 drives in RAIDZ2, your pool will be able to survive the failure of any 2 drives without data loss, and the ZFS police will give you a pony." Robert Trevellyan

 

[Naesstrom]

Ok so I'm convinced but the only free drives I have is the new 6TB ones. I'm thinking of doing something like this but I'm not sure how.
1. connect the 2 6TB drives as a new voolume
2. Move everything from the old volume to the new one
3. Delete the old volume and create a new one from the 4x4tb drives in raidz2
4. Move back everything to the new volume
5. delete the 6TB volume and add the drives to the new one

 

[Ericloewe]

delete the 6TB volume and add the drives to the new one

That would not get you a sensible configuration. It'd be a rather silly idea, even.

 

[Naesstrom]

That would not get you a sensible configuration. It'd be a rather silly idea, even.

Oh but I thought that was what's being suggested above, create a raidz2 volume with all 6 disks? And then if I replace the 4x4TB one's in the future I'll have the best config.
TBH I'm feeling like just adding the 2 new 6TB's to the current volume and mirror them, just feel like I'm wasting a lot of space that maybe I didn't need to!

 

[gpsguy]

Unfortunately, after you create the 4 drive RAIDZ2 vdev, you can't add additional drives to that same vdev. You can create additional vdev's and extend your volume with them,

In your case, you might end up with a volume cons ting of a 4 disk RAIDz2 vdev and a 2 disk mirrored vdev. You shouldn't mix vdev types in a volume. In this example, the mirror would be the weak link.

Sent from my iPhone using Tapatalk

 

[Naesstrom]

*sigh* so right now since I don't have any space somewhere else to store the contents I'm screwed?
I'll just add the 2 new disks mirrored right now and then in a few months when I can buy 4 more 6tb disks see if I can redo it then.

Sent from my Nexus 6P using Tapatalk

 

[gpsguy]

Yes.

At least you understand the problem and didn't make a stupid mistake. We often see users that had great pool designs (RAIDz2, etc) and tried to add a single drive. They figure out how to do it and then discover that they need to backup 20+TB of data somewhere, so they destroy their pool and start over.

*sigh* so right now since I don't have any space somewhere else to store the contents I'm screwed?

 

[ttabbal]

Or just use mirrors. For home users that often can't buy 6+ disks at a time, mirrors can work well. You also get more performance, though if that matters in your specific case is up to you. But the up side is easy expansion and much faster reslivers. You can add/replace 2 drives at a time. You can also upgrade without sacrificing parity as well, just add a larger drive to the mirror, wait for it to replicate, then remove the old one.

The down side is you need to closely monitor the drives and not wait to replace drives that are failing. If you see SMART errors creeping up, replace immediately. You should do that with raidz2 as well, but home users tend to let it slide a bit.

After you get a replacement in, do the burn in tests on the old one. If it passes, you have a spare, a drive to use somewhere else, etc..

Your current configuration is sane, redundant, and even preferred for some workloads. It's not as space efficient, but it is more flexible and faster. At least you didn't add a single non redundant drive to the pool.

 

[Robert Trevellyan]

I'll just add the 2 new disks mirrored right now

Do this. Mirrors appear to have have served you well this far, just go with it.

RAIDZ2 is more reliable, but you said...

I don't feel that redundancy is all that important anymore

Just make sure your SMART service and tests and email notifications are working properly, and burn in those new drives before deploying them.

feel like I'm wasting a lot of space

If you can adopt the mindset of "using 50% of my raw storage to deliver redundancy, performance and flexibility", it might not seem so bad.

You can also upgrade without sacrificing parity as well, just add a larger drive to the mirror, wait for it to replicate, then remove the old one.

Adding a drive to a mirror, then removing it later, requires command-line intervention, which is undesirable. The documentation describes an easier way (for any vdev configuration), assuming you have at least one spare drive port.