Dissimilar data VDEVs in a pool

[Peter Blanchard]

I've read TrueNAS documentation, looked on various forums, etc but still a bit confused.

I've 4 x 600GB SAS 10k rpm HDDs,
And 4 x 900GB SAS 10k rpm HDDs.
I'll set them up as two RAID-Z1 vdevs.

I can put them in the same pool? If so, what are the advantages/disadvantages?

Would I be better off creating two separate pools?

What do I need to think about when adding more vdevs to a pool?

Also, I have three Intel 120GB DC S3500 SSDs. How can I best use them?

Machine has Supermicro X10SLH-LN6TF motherboard, 32GB RAM. Going to be direct attached by aggregrated 10gig ethernet to couple of PCs and well as gigabit for lesser machines. Not quite there yet but will be doing low-end audio/video experiments with the PCs. They've got 512GB NVMe drives in them, but video will quickly eat that up.

 

[BackupProphet]

Yes you can. You can create 2 raidz vdevs where you stripe both vdevs, of course when you use more than 66% of the available pool it will start getting imbalances. You will get excellent performance and since the drives small in size, rebuild speed will be fast.
I would use the Intel SSD's as special metadata devices. If you add them as 3 way mirror you can set redundant_metadata to none and effectively get twice the metadata space.

 

[Peter Blanchard]

Thanks.

So you'd not recommend using the SSDs as L2ARC?

I'm very new to this.

 

[mr44er]

So you'd not recommend using the SSDs as L2ARC?

Before using/thinking about L2ARC, you should upgrade RAM to the max (32G isn't much). Thing is, L2ARC eats a portion of RAM (bigger L2ARC eats more RAM) to address what and where...likely that you in the end get the opposite what you want to achieve.
You will profit more from 64G alone than from 32G with L2ARC.

 

[mr44er]

Also, I have three Intel 120GB DC S3500 SSDs. How can I best use them?

See this as one of the different options what I would do.
I would use them as 3x zfs mirror and install only the TrueNAS system on it. The system will boot fast and runs even if 2 of them die.

The other disks:
I don't use raidz1 anymore, I want more redundancy. If during a running resilver another disk dies, which is not unlikely, the whole pool is gone.
More or less the same question which config is good: https://forums.servethehome.com/index.php?threads/raidz1-hotspare-question-enlightenment.40411/

These 600 and 900er disks are over 10 years old, so I would do a raidz2 pool with all of them (1x vdev). Yes, this makes 4x300GB go *poof*, but it gives adequate redundancy/safety for these old disks and it's likely that you replace them anyway in the near future, because you need more capacity and it moves out some complexity.

This gives you (8*600 brutto) - (2*600 for redundancy) = 3600GB netto capacity and 2 disks can die.
If you replace them all after another with more modern 2TB disks, you can grow the pool and you'll get 12000GB (6*2000) netto.
With 4TB = 24000GB

You could do your raidz1 with 2 pools. This gives you one pool with 1800GB (3*600) and another with 2700GB (3*2700). In both pools only one disk can die.

You can group them together via 2 raidz1-vdevs. vdev1 1800GB (3*600) + vdev2 2700GB (3*900) = 4500GB netto. This gives you more IOPS (more vdevs in a pool = more IOPS). You can loose 2 disks, but only one per vdev. If you loose 2 disks in vdev1 or vdev2, the whole pool is gone.

So it's up to you what you want...or not.

 

[Peter Blanchard]

Thank you all.

Because HDDs were packed away, I'd mis-remembered the number of drives I had. Not all of them display capacity on label but 16 rather than 8 in total.

 

[T_Minus]

Another thought... you can get 1.92TB SATA Enterprise SSD (slower\older but faster than HDD) on ebay for $45.

Why not sell\recycle the group of HDD and just get a couple of these to replace the slower, older, power-hungry HDD?

You'll have more performance than the HDD , lower power and no moving parts

 

[Peter Blanchard]

You can't get them that cheap on eBay.co.uk!!! £65 is the cheapest I've found. Nor can I find any cheaper from other places.

I don't have the budget for an all SSD NAS yet. Nor do I have a pressing need (yet).

 

[BoredSysadmin]

I've read TrueNAS documentation, looked on various forums, etc but still a bit confused.

I've 4 x 600GB SAS 10k rpm HDDs,
And 4 x 900GB SAS 10k rpm HDDs.
I'll set them up as two RAID-Z1 vdevs.

I can put them in the same pool? If so, what are the advantages/disadvantages?

Would I be better off creating two separate pools?

What do I need to think about when adding more vdevs to a pool?

Also, I have three Intel 120GB DC S3500 SSDs. How can I best use them?

Machine has Supermicro X10SLH-LN6TF motherboard, 32GB RAM. Going to be direct attached by aggregrated 10gig ethernet to couple of PCs and well as gigabit for lesser machines. Not quite there yet but will be doing low-end audio/video experiments with the PCs. They've got 512GB NVMe drives in them, but video will quickly eat that up.

32GB ram should be plenty; ideally, it's ECC, but it's not critical. But your most significant issue is these ancient and tiny hard drives - I'd not recommend using them for anything other than short-term lab/experiment. They are very small, slow, and power-hungry. You'd better off buying a pair of 10TB 7.2k Sata drives and mirroring them - you would double the space, use only 1/5 of the power (7.2k rpm drives use less power than 10k ones), and likely improve sequential performance anyhow.

 

[Peter Blanchard]

It is ECC low profile memory.

I've more drives than I thought. Double what I initially said.

Also, I bought ten second user 3TB 7.2k SAS drives for another build.