ZFS Z2 performance with respect to number of disks

[Kiran Kankipati]

Hi

I got a question on ZFS Z2 performance with respect to number of disks.
Let us assume each disk is 1TB in size put inside a ZFS Z2 pool.

Can you give me some insight about the overall read and write performance if configured
5x 1TB (Z2) vs
6x 1TB (Z2) vs
7x 1TB (Z2) vs
8x 1TB (Z2)

may I know which one is going to be faster ?
5 drives, or 6 drives, or 7 or 8 within the pool

 

[Chris Moore]

RAIDz2, not ZFS Z2. The ZFS file system on disk is made up of one or more vdevs and each vdev can be either a mirror of two (or more) disks, or a vdev can be RAIDz1 (often simply called RAIDz), RAIDz2 or RAIDz3. Regardless of the configuration of each vdev in a storage pool, the pool performance is based (generally speaking) on the number of vdevs, not on the composition of an individual vdev in the pool. This is a very large generalization, but the rule is that each vdev has roughly the performance of a single member disk in the vdev.

The thing you should do is tell us what you want to do with your storage and ask us what the best pool configuration is. There are many forum members that use FreeNAS in their work environment and have a great deal of experience optimizing for various workloads.

 

[Kiran Kankipati]

Thank you Chris. Let me have a look :)

 

[z2Dylan]

RAIDz2, not ZFS Z2. The ZFS file system on disk is made up of one or more vdevs and each vdev can be either a mirror of two (or more) disks, or a vdev can be RAIDz1 (often simply called RAIDz), RAIDz2 or RAIDz3. Regardless of the configuration of each vdev in a storage pool, the pool performance is based (generally speaking) on the number of vdevs, not on the composition of an individual vdev in the pool. This is a very large generalization, but the rule is that each vdev has roughly the performance of a single member disk in the vdev.

The thing you should do is tell us what you want to do with your storage and ask us what the best pool configuration is. There are many forum members that use FreeNAS in their work environment and have a great deal of experience optimizing for various workloads.

If a single vdev has roughly the same performance as a single disk, then why are speeds improved with more disks in this test? https://calomel.org/zfs_raid_speed_capacity.html

 

[sretalla]

If a single vdev has roughly the same performance as a single disk, then why are speeds improved with more disks in this test?

See my answer here:

Pool build performance question..

I currently have 5 10TB WD Reds in Z2 and looking to rebuild my pool soon with performance being not very important, but certainly a consideration. My understanding is you can (roughly) subtract 2 disks from your pool (Z2) and multiply the rest of the disks by their read/write speeds to get a...

www.truenas.com

 

[Chris Moore]

If a single vdev has roughly the same performance as a single disk, then why are speeds improved with more disks in this test? https://calomel.org/zfs_raid_speed_capacity.html

As I said,

This is a very large generalization

The general rule is, if you want more IOPS, you need more vdevs. The system I have at work right now has 82 vdevs for speed. Each of those is RAIDz2, so it is a lot of disks, but the number of disks in ther is mostly for capacity. We have about 8 PB of online storage and it is pretty quick.

The speed of each vdev does improve marginally with the number of disks in the vdev, but the more dramatic improvement is by increasing the vdev count, which is why using mirrors is usually the way to get fast storage/high IOPS. It really depends on what you are trying to acomplish. Like I said in the previous answer, if you can tell us what you are after, we can suggest some hardware.