Pool Creation using WWNs

TrueNAS General
1

It seems fairly common practice outside of TrueNAS that when building pools from a CLI to use WWNs like /dev/disk/by-id/wwn-0x5000cca1234a1234 instead of block device files like /dev/sda at pool creation. This can often be helpful identifying drives during disk replacement procedures. As this is often an area of confusion with TrueNAS users I wondered if there was any technical reason why by default TrueNAS couldn’t do this when building pools from within the UI?

I’d be interested in all your thoughts on this.

2

Are the WWN ids any less confusing than the partition UUIDs that TrueNAS uses? Neither is particularly intuitive, and both require translating to actual serial numbers.

3

Well they are often printed on the drive itself which is a better start :wink:

1 Like
4

Sometimes the sda, sdb etc will change between reboots

5

Exactly my point whereas WWN will not.

6

Well, that may be true, but TrueNAS doesn’t use block device files when creating data pools.

It uses GPT UUIDs, which seem to be an equally valid choice, with the benefit of being able to clone drives if necessary.

7

True although block device files are shown via the UI. I always found that strange how zpool status from CLI would appear different to the equivalent in the UI.

The problem with GPT UUIDs is that they give the user no clue as to which physical drive is located where however with WWD you have a direct relationship.

When you say the benefit of being able to clone drives how do you mean?

8

A WWN is locked to a physical piece of hardware.

A UUID can be cloned from one drive to another, for example as part of a data recovery scenario.

Unless there is a reason to actually lock a partition to a physical device (and there normally isn’t) then I think WWNs shouldn’t be used

9

Exactly that’s the beauty.

Ah ok but I can’t see this being used often by the average TN user compared to how helpful knowing where a failing/failed drive is in your system.

The idea comes from my experience that disk identification is quite possibly the number 1 issue I see TN users having and anything we can do to assist them in this regard is a massive plus in my book.