ZFS Storage Pool Layout 2024-03-14

[Davvo]

Davvo submitted a new resource:

ZFS Storage Pool Layout - iX's White Paper

This amazing document, created by iX System in February 2022 as a "White Paper", cleanly explains how to qualify pool performance touching briefly how ZFS stores data and presents the advantages, performance and disadvantages of each pool layout (striped vdev, mirrored vdev, raidz vdev).
It also offers three common scenarios highlighting the different needs, weaknesses and solutions.

Reading the Introduction to...

Read more about this resource...

 

[NugentS]

I have one issue with the doc - it mentions SLOG as a write cache

"There are two special vdev types that we have not discussed: an L2ARC and a SLOG. These special vdevs can be added to a pool to function as a read cache and a write cache, respectively"

SLOG is not a write cache

 

[Davvo]

I agree, especially when phrased in a way that basically means "they are the same thing".

However, a simple search on this forum should be enough for anyone to clear the misunderstanding.

Should I include a warning in the resource description? It's not really the focus of the paper though, and it's mentioned briefly.

 

[Davvo]

Unless I am forgetting something big, I found a few math errors.

The first in page 5, 6x 2-way mirror: both the read and write IOPS are wrong.
Since the single-disk IOPS the paper set is 250, a 2-way mirror gets 500 read IOPS and 250 write IOPS: 6 vdevs of such mirror brings us to 3000 read IOPS and 1500 write IOPS; the paper reports 1200 and 600 instead (which are the read and write speeds).

The second in page 6, 4x 3-way mirror: the read speed is 1200 instead of the reported 3000.

Will add an errata and a reference to the ZIL/SLOG resource.

 

[Davvo]

Davvo updated ZFS Storage Pool Layout with a new update entry:

ERRATA

While the resource is valid there are a few mistakes, namely:

• page 4, Storage space efficiency formula:
  • correct: 1/N​
• page 5, 6x 2-way mirror
  • correct Read IOPS: 3000​
  • correct Write IOPS: 1500​
• page 6, 4x 3-way mirror
  • correct Streaming read speed: 1200 MB/s​
• page 11, Scenario 3​
  • a...​

Read the rest of this update entry...

 

[Davvo]

Davvo updated ZFS Storage Pool Layout with a new update entry:

ZFS Storage Layout Whitepaper v2.0

Thanks to @HoneyBadger iX Systems updated the old resource by fixing the errors and further improving it. I have thus removed the option to download the old PDF from this resource, and uploaded at this link for posterity.

Show : OLD VERSION's ERRATA

While the resource is valid there are a few mistakes, namely:

• page 4, Storage space efficiency formula
  • ...

Read the rest of this update entry...