RAIDZ2 with 5 Drives - Performance?

[citrate]

Hello there! I used to utilize a mini PC for network storage and am planning to upgrade to a "real" NAS recently. I decided to build a NAS PC from scratch, with a 5-HDD-slot chassis, and to use TrueNAS and RAIDZ. I'm planning to use five "second-hand retired enterprise-level E-waste 14 TB hard drives" to save my budget. For the safety of my data, I decided to use RAIDZ2 (They are e-waste!). Then I found these posts stating that there are performance issues using RAIDZ2 on 5 hard drives:

VDEV raidz2 with five disks

I read a lot about optimal configurations, but I did not find a concrete listing of disadvantages, when not using an optimal number of disks. The problem is that the most motherboards have only 6 SATA-ports and, if you want to use a SSD for OS and jails, there are only five ports remaining. For...

www.truenas.com

5 disk raidz2

The largest number of drives for my NAS rig as currently planned is a total of 5 disks and I would like the protection of raidz2. This is the limit for two reasons: The case I want badly can only support 5 disks without modding, and the motherboard for this build only supports 4 disks; a...

www.truenas.com

RAIDZ2 with 7 Disks?

Most discussions of RAIDZ2 refer to 6 or 10 disks as ideal. Is there a significant (or for that matter any) penalty to using 7 drives (7 x 3TB) in a RAIDZ2 configuration? Thanks.

www.truenas.com

RAIDz Suggested Number of Drives For Maximum Performance

I've been trying to understand why there are recommended numbers of drives for ZFS RAIDz Vdevs. I found this thread: What number of drives are allowed in a RAIDZ config? which suggests this is because ZFS writes 128KIB blocks and drives in other than the recommended n^2-parity cause the system...

www.truenas.com

From those posts, it seems that the block size or stripe size or something in RAIDZ2 is not optimal for 5 disks? But about 10 years have passed since these posts! I wonder is there any improvement of ZFS on this so that there's no longer a performance issue for RAIDZ2 on 5 drives? Or, if the issue persists, is it as bad as the past?

 

[Arwen]

Welcome to the forums!

See this article, written by one of the designers & writers of ZFS;

ZFS RAIDZ stripe width, or: How I Learned to Stop Worrying and Love RAIDZ | Perforce Software

The popularity of OpenZFS has spawned a great community of users, sysadmins, architects and developers, contributing a wealth of advice, tips and tricks, and rules of thumb on how to configure ZFS.

www.delphix.com

 

[jgreco]

But about 10 years have passed since these posts! I wonder is there any improvement of ZFS on this so that there's no longer a performance issue for RAIDZ2 on 5 drives?

The fundamentals don't change just because time passes. The common car of today goes about as fast as the common car of ten years ago.... it's just the way that the physics and science work out.

RAIDZ is optimized for large sequential file storage, with a relatively small number of simultaneous accesses. It maximizes the available storage by using RAID rather than mirroring, and maximizes the recoverability by using a better RAID parity scheme. The cost is that this causes more drives to be involved in many pool accesses. Until this changes, and it isn't likely to change, you're going to be limited by head seek times and other similar factors.

 

[citrate]

Welcome to the forums!

See this article, written by one of the designers & writers of ZFS;

ZFS RAIDZ stripe width, or: How I Learned to Stop Worrying and Love RAIDZ | Perforce Software

The popularity of OpenZFS has spawned a great community of users, sysadmins, architects and developers, contributing a wealth of advice, tips and tricks, and rules of thumb on how to configure ZFS.

www.delphix.com

Thanks! Just finished reading. I think TL;DR for me is “use compression, choose whatever Z1 or Z2 depending on my confidence on the disks”, right? :)

 

[Arwen]

Thanks! Just finished reading. I think TL;DR for me is “use compression, choose whatever Z1 or Z2 depending on my confidence on the disks”, right? :)

Yes, that sums it up.

If you have good backups and want to risk RAID-Z1 with larger disks, then that is fine.
On the other hand, if you don't have good backups, then perhaps RAID-Z2 would be a better choice.