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Docs: Clarify APFS trim situation

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vit9696 2021-01-30 20:31:51 +03:00
parent 8d49815141
commit 7cc3e8ad12
5 changed files with 67 additions and 23 deletions
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@ -2563,18 +2563,39 @@ blocking.
\textbf{Requirement}: 10.14 (not required for older)\\
\textbf{Description}: Set trim timeout in microseconds for APFS filesystems on SSDs.
Depending on the SSD controller trim procedure may take considerable
amount of time, causing noticeable boot slowdown as this is when the
APFS driver executes the trim operation. If the SSD supports
over-provisioning or there exists a dedicated unused partition that
can be used to reserve blocks, trim operation may not be necessary.
On the other side if the SSD is slow, the default timeout (equals to
\texttt{9.999999} seconds) may not be enough. See more details
in this \href{https://interface31.ru/tech_it/2015/04/mozhno-li-effektivno-ispolzovat-ssd-bez-podderzhki-trim.html}{article}.
APFS filesystem is designed in a way that the space controlled via
spaceman structure is either used or free. This may be different in
other filesystems where the areas can be marked as used, free, and
\emph{unmapped}. All free space is trimmed (unmapped/deallocated)
at macOS startup. The trimming procedure for NVMe drives happens
in LBA ranges due to the nature of \texttt{DSM} command with
up to 256 ranges per command. The more fragmented the memory
on the drive is, the more commands are necessary to trim all the
free space.
Set this value to \texttt{4294967295} for the maximum timeout to
guarantee trim success or to \texttt{999} to essentially disable
trim.
Depending on the SSD controller and the drive fragmenation trim procedure
may take considerable amount of time, causing noticeable boot slowdown
APFS driver explicitly ignores previously unmapped areas and trims
them on boot again and again. To workaround boot slowdown macOS
driver introduced a timeout (\texttt{9.999999} seconds) that stops
trim operation when it did not manage to complete in time. On many
controllers, such as Samsung, where the deallocation is not very fast,
the timeout is reached very quickly. Essentially it means that
macOS will try to trim all the same lower blocks that have already been
deallocated, but will never have enough time to deallocate higher blocks
once the fragmentation increases. This means that trimming on these SSDs
will be broken soon after the installation, causing extra wear to the flash.
One way to workaround the problem is to increase the timeout to a very
high value, which at the cost of slow boot times (extra minutes)
will ensure that all the blocks are trimmed. For this one can set
this option to a high value, e.g. \texttt{4294967295}.
Another way is to utilise over-provisioning if it is supported or create
a dedicated unmapped partition where the reserve blocks can be found
by the controller. In this case the trim operation can also be disabled
by setting a very low timeout. e.g. \texttt{999}. See more details
in this \href{https://interface31.ru/tech_it/2015/04/mozhno-li-effektivno-ispolzovat-ssd-bez-podderzhki-trim.html}{article}.
\item
\texttt{ThirdPartyDrives}\\

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@ -1,7 +1,7 @@
\documentclass[]{article}
%DIF LATEXDIFF DIFFERENCE FILE
%DIF DEL PreviousConfiguration.tex Fri Jan 22 17:04:29 2021
%DIF ADD ../Configuration.tex Sat Jan 30 09:06:04 2021
%DIF ADD ../Configuration.tex Sat Jan 30 20:30:16 2021
\usepackage{lmodern}
\usepackage{amssymb,amsmath}
@ -2624,19 +2624,42 @@ blocking.
\textbf{\DIFadd{Description}}\DIFadd{: Set trim timeout in microseconds for APFS filesystems on SSDs.
}
\DIFadd{Depending on the SSD controller trim procedure may take considerable
amount of time, causing noticeable boot slowdown as this is when the
APFS driver executes the trim operation. If the SSD supports
over-provisioning or there exists a dedicated unused partition that
can be used to reserve blocks, trim operation may not be necessary.
On the other side if the SSD is slow, the default timeout (equals to
}\texttt{\DIFadd{9.999999}} \DIFadd{seconds) may not be enough. See more details
in this }\href{https://interface31.ru/tech_it/2015/04/mozhno-li-effektivno-ispolzovat-ssd-bez-podderzhki-trim.html}{\DIFadd{article}}\DIFadd{.
\DIFadd{APFS filesystem is designed in a way that the space controlled via
spaceman structure is either used or free. This may be different in
other filesystems where the areas can be marked as used, free, and
}\emph{\DIFadd{unmapped}}\DIFadd{. All free space is trimmed (unmapped/deallocated)
at macOS startup. The trimming procedure for NVMe drives happens
in LBA ranges due to the nature of }\texttt{\DIFadd{DSM}} \DIFadd{command with
up to 256 ranges per command. The more fragmented the memory
on the drive is, the more commands are necessary to trim all the
free space.
}
\DIFadd{Set this value to }\texttt{\DIFadd{4294967295}} \DIFadd{for the maximum timeout to
guarantee trim success or to }\texttt{\DIFadd{999}} \DIFadd{to essentially disable
trim.
\DIFadd{Depending on the SSD controller and the drive fragmenation trim procedure
may take considerable amount of time, causing noticeable boot slowdown
APFS driver explicitly ignores previously unmapped areas and trims
them on boot again and again. To workaround boot slowdown macOS
driver introduced a timeout (}\texttt{\DIFadd{9.999999}} \DIFadd{seconds) that stops
trim operation when it did not manage to complete in time. On many
controllers, such as Samsung, where the deallocation is not very fast,
the timeout is reached very quickly. Essentially it means that
macOS will try to trim all the same lower blocks that have already been
deallocated, but will never have enough time to deallocate higher blocks
once the fragmentation increases. This means that trimming on these SSDs
will be broken soon after the installation, causing extra wear to the flash.
}
\DIFadd{One way to workaround the problem is to increase the timeout to a very
high value, which at the cost of slow boot times (extra minutes)
will ensure that all the blocks are trimmed. For this one can set
this option to a high value, e.g. }\texttt{\DIFadd{4294967295}}\DIFadd{.
}
\DIFadd{Another way is to utilise over-provisioning if it is supported or create
a dedicated unmapped partition where the reserve blocks can be found
by the controller. In this case the trim operation can also be disabled
by setting a very low timeout. e.g. }\texttt{\DIFadd{999}}\DIFadd{. See more details
in this }\href{https://interface31.ru/tech_it/2015/04/mozhno-li-effektivno-ispolzovat-ssd-bez-podderzhki-trim.html}{\DIFadd{article}}\DIFadd{.
}
\item

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