FAQ: TRIM: GELI, ZFS, OpenZFS: pruning, tidiness

[grahamperrin]

Summary

Key points:

• the ViewVC views of 2013 Subersion revisions are no longer of interest
• vfs.zfs.trim.enabled is unknown in FreeBSD 13.1-RELEASE-p3.

Affected:

• https://docs.freebsd.org/en/books/faq/#zfs-ssd-trim.

Related bug report:

• PR 261212

… Update the ZFS chapter (20) of the FreeBSD Handbook, and other OpenZFS-related pages

Origin of this diff:

• https://github.com/grahamperrin/freebsd-doc/tree/faq.

Test Plan

Preview in GitHub:

• https://github.com/grahamperrin/freebsd-doc/blob/faq/documentation/content/en/books/faq/_index.adoc#97-is-there-trim-support-for-zfs-on-solid-state-drives.

[pauamma_gundo.com]

documentation/content/en/books/faq/_index.adoc

1598

s/incuded/included/

1609

Do 2-item lists take a comma when the items are this short?

[grahamperrin]

documentation/content/en/books/faq/_index.adoc

1598

Done in GitHub. It'll be included with a commit.

1609

Advice might vary.

The intention here is to pause.

Technical readers who are familiar with manual pages will be OK without a comma.

For a less technical reader, at a glance, there's potential ambiguity without the comma in the second part of the sentence:

Blah in blah and blah: x and y in z.

https://www.bartleby.com/141/strunk.html#2 in Rules of Usage. Strunk, William, Jr. 1918. Elements of Style.

https://www.thesaurus.com/e/grammar/commas-and-conjunctions/#before-or-after-and in When To Use Commas With Conjunctions | Thesaurus.com.

Do You Need Commas Before Conjunctions? - The Blue Book of Grammar and Punctuation at grammarbook.com.

[mav]

Looks good to me, but I am not sure it makes sense to still have the paragraph about 11.0. 11 branch is out of support now, plus that -T option of geli seems to disable TRIM, not enable it, that would have some more sense to document.

[delphij]

documentation/content/en/books/faq/_index.adoc

1598

I think this should be moved somewhere below. ZFS TRIM/UNMAP requires a GEOM provider that supports TRIM/UNMAP, which can be a raw disk device, a partition, and not limited to GELI.

The two are two different, orthogonal topics.

1599

It should be mentioned (e.g. "See risks of doing this and how to disable it with man:geli[8] option -T") that there is a risk of enabling TRIM on GELI providers, because by doing so the backing sectors would read back as zeros, indicating that there is no useful data.

1609

another suggestion is that we should say that this is the preferred way of enabling or disabling TRIMs.

The reason is that it would behave consistently in different OpenZFS implementations and it also enables fine grained control; with the loader environment it would be a global flag that applies to all pools.

[grahamperrin]

Comment https://reviews.freebsd.org/D37512#852949: done.

Whilst here, I noticed:

• some quotes where surrounding apostrophes were obviously missing
• a few missing full stops.

Also whilst here: AsciiDoc line breaks.

[grahamperrin]

documentation/content/en/books/faq/_index.adoc

1598

I think this should be moved somewhere below. ZFS TRIM/UNMAP requires a GEOM provider that supports TRIM/UNMAP, which can be a raw disk device, a partition, and not limited to GELI.

The two are two different, orthogonal topics.

With regard to the original NOTE box:

ZFS TRIM support was added to GELI … see man:geli[8] and the -T switch.

– nowadays, I doubt that this is truly a frequently asked question or answer.

---

If the essence of the original note is not already in a manual page, or the FreeBSD Handbook, then it might be better to have the essence there (away from FAQ).

1599

It should be mentioned (e.g. "See risks of doing this and how to disable it with man:geli[8] option -T") that there is a risk of enabling TRIM on GELI providers, because by doing so the backing sectors would read back as zeros, indicating that there is no useful data.

Correct me, please, if I'm wrong: I get the impression that this type of thing is relatively obscure (neither frequently asked, nor frequently answered).

IMHO the manual page is the ideal place to express risks.

[grahamperrin]

Orientation (since inline comments have become misplaced):

• the essence of this review – originally section "9.7. Does ZFS support TRIM for Solid State Drives?" – is now lines 1626–1637.

[delphij]

documentation/content/en/books/faq/_index.adoc

1599

Yes, the latest revision is reasonable.

[grahamperrin]

Approved by: delphij (doc)

Sorry, dyslexia (and inconsistencies between examples). That should have been:

Approved by: doc (delphij)

I did look closely under https://docs.freebsd.org/en/articles/committers-guide/#_include_appropriate_metadata_in_a_footer a few minutes before the commit:

– but then, thoughts became disorderly whilst seeking a commit team name to match the ZFS group, of which delphij is a member; also whilst trying to remember which commit team name relates to Doc committers (not to be confused with docs).

For the latter, I used https://cgit.freebsd.org/doc/log/?qt=grep&q=%28doc%29 to plug the hole in my memory. I ignored the (doc) listings, focused instead on the most recent example, which includes this:

Approved by: carlavilla (doc)

– I guess that should have been:

Approved by: doc (carlavilla)