VDEV Pool Support

[vdev-noob-55]

Hi Guys,

I'm pretty new to truenas and recently just purchased 12 Drives that I'm passing through to truenas scale. The drives are 1.2TB 12gb SAS drives and I've grouped them into 1 Zdev running raidz3. It's recently come to my attention that it's good practice to only limit a pool to around 10 drives. Would it be worth my wild to split the VDEV and create 2 VDEV's with 6 disks running RAIDZ2. Would this gain much performance and would you guys reccomend this. Also is there any procedure to splitting a VDEV into 2? It's not too much of an issue if there isn't there is only really around 50GB of data in the pool as of the moment so worst case I can pull all the data off and create 2 ZDEV's from scratch. Just seeking some opinions on this and if this is worth my wild or recommended.

Appreciate any advice. Hope everyone is enjoying their weekend

 

[Arwen]

First off, "Zdev" is really "vDev", for Virtual Device.

Next, 12 disks is okay for a RAID-Z2/3 vDev. It just depends on what you are trying to accomplish, more storage, or faster IOPS. You have to choose.

No, their zero method to split a 12 disk RAID-Zx vDev, or remove disks from a RAID-Zx vDev. It's backup, destroy and create new.

 

[vdev-noob-55]

thanks for your response ! Apologies for the mix-up between Zdev and vDev I am really most likely after more storage as they really are only 1.2tb drives. Is there any way to calculate or estimate the difference between IOPS

 

[vdev-noob-55]

thanks for your response ! Apologies for the mix-up between Zdev and vDev I am really most likely after more storage as they really are only 1.2tb drives. Is there any way to calculate or estimate the difference between IOPS

between say a 12 Disk vDev and two 6 disk vDev's

 

[Arwen]

A RAID-Zx vDev has the IOPS, (I/O Operations Per Second), of a the slowest disk in the vDev. This is because a RAID-Zx write stripes across all the disks in a vDev, (generally). Thus, has to wait for the slowest disk in the vDev to complete it's write before it can write another stripe.

A 2 vDev RAID-Zx pool will have combined more IOPS, based on the slowest disk for each vDev. ZFS will write to one stripe, then if the other vDev is not full, schedule the next write to the other vDev. Then back and forth. So faster writes.

However, if the RAID-Zx vDevs are very imbalanced, like one vDev is 80% full and the other vDev is 20% full, ZFS will favor the less full one. This can happen if you "grow" your pool by adding a new vDev. ZFS will eventually balance the vDev usage out over time, (assuming it is not static data).

I don't really have knowledge to calculate or estimate the difference.

 

[Davvo]

Please read the following resources.

Introduction to ZFS

This is a short introduction to ZFS. It is really only intended to convey the bare minimum knowledge needed to start diving into ZFS and is in no way meant to cut Michael W. Lucas' and Allan Jude's book income. It is a bit of a spiritual...

www.truenas.com

ZFS Storage Pool Layout

This amazing document, created by iXsystems in February 2022 as a "White Paper", cleanly explains how to qualify pool performance touching briefly on how ZFS stores data and presents the advantages, performance and disadvantages of each pool...

www.truenas.com

You can find more in my signature.