Page MenuHomeFreeBSD
Differential D27715 Diff 81379 en_US.ISO8859-1/books/handbook/zfs/chapter.xml

Changeset View

Standalone View

View Options

en_US.ISO8859-1/books/handbook/zfs/chapter.xml

Show First 20 Lines • Show All 2,920 Lines • ▼ Show 20 Linesmypool/compressed_dataset logicalused 496G -</screen>
compression caused them to reach their quota limit.</para> compression caused them to reach their quota limit.</para>
<para>Compression can have a similar unexpected interaction with <para>Compression can have a similar unexpected interaction with
backups. Quotas are often used to limit how much data can be backups. Quotas are often used to limit how much data can be
stored to ensure there is sufficient backup space available. stored to ensure there is sufficient backup space available.
However since quotas do not consider compression, more data However since quotas do not consider compression, more data
may be written than would fit with uncompressed may be written than would fit with uncompressed
backups.</para> backups.</para>
<sect3 xml:id="zfs-zfs-compression-zstd">
<title>Zstandard Compression</title>
<para>In <acronym>OpenZFS</acronym> 2.0, a new compression
algorithm was added. Zstandard (<acronym>Zstd</acronym>)
offers higher compression ratios than the default
<acronym>LZ4</acronym> while offering much greater speeds
than the alternative, <acronym>gzip</acronym>.
<acronym>OpenZFS</acronym> 2.0 is available starting with
&os;&nbsp;12.1-RELEASE via
<package>sysutils/openzfs</package> and has been the
default in &os;&nbsp;13-CURRENT since September 2020, and
debdrupUnsubmitted
Not Done
Inline Actions

Should this be "is the default as of FreeBSD 13-CURRENT and will be in 13.0-RELEASE"?

debdrup: Should this be "is the default as of FreeBSD 13-CURRENT and will be in 13.0-RELEASE"?
will by in &os;&nbsp;13.0-RELEASE.</para>
<para><acronym>Zstd</acronym> provides a large selection of
compression levels, providing fine-grained control over
performance versus compression ratio. One of the main
pauamma_gundo.comUnsubmitted
Done
Inline Actions

After the initial introduction of both "Zstandard" and its acronym "Zstd", I'd use one consistently, not a mix of both.

pauamma_gundo.com: After the initial introduction of both "Zstandard" and its acronym "Zstd", I'd use one…
allanjudeAuthorUnsubmitted
Done
Inline Actions

Done

allanjude: Done
advantages of <acronym>Zstd</acronym> is that the
decompression speed is independent of the compression
level. For data that is written once but read many times,
emasteUnsubmitted
Done
Inline Actions

I wonder if it would be clear to say no advantage to lower compression levels to avoid the double negative. Or something like "but read many times, Zstd allows the use of high compression levels without a performance penalty."

emaste: I wonder if it would be clear to say no advantage to lower compression levels to avoid the…
emasteUnsubmitted
Done
Inline Actions

mmm, reading it again, maybe we should mention without a "read" performance penalty?

emaste: mmm, reading it again, maybe we should mention without a "read" performance penalty?
allanjudeAuthorUnsubmitted
Done
Inline Actions

agreed

allanjude: agreed
<acronym>Zstd</acronym> allows the use of the highest
compression levels without a read performance
penalty.</para>
<para>Even when data is updated frequently, there are often
performance gains that come from enabling compression. One
of the biggest advantages comes from the compressed ARC
pauamma_gundo.comUnsubmitted
Not Done
Inline Actions

Clarification: here and in the following paragraph, is it ZFS or OpenZFS?

pauamma_gundo.com: Clarification: here and in the following paragraph, is it ZFS or OpenZFS?
allanjudeAuthorUnsubmitted
Done
Inline Actions

They are fairly synonymous, I think we'll have to do an entire pass over the handbook at some point

allanjude: They are fairly synonymous, I think we'll have to do an entire pass over the handbook at some…
feature. <acronym>ZFS</acronym>'s Adaptive Replacement
Cache (<acronym>ARC</acronym>) caches the compressed version
debdrupUnsubmitted
Done
Inline Actions

s/cache/memory/

debdrup: s/cache/memory/
debdrupUnsubmitted
Done
Inline Actions

s/cache/memory/

Or better yet:
<acronym>RAM</acronym> instead of the word cache or the word memory.

debdrup: > s/cache/memory/ Or better yet: <acronym>RAM</acronym> instead of the word cache or the word…
of the data in <acronym>RAM</acronym>, decompressing it each
time it is needed. This allows the same amount of
<acronym>RAM</acronym> to store more data and metadata,
increasing the cache hit ratio.</para>
<para><acronym>ZFS</acronym> offers 19 levels of
<acronym>Zstd</acronym> compression, each offering
incrementally more space savings in exchange for slower
compression. The default level is
<literal>zstd-3</literal> and offers greater compression
than <acronym>LZ4</acronym> without being significantly
slower. Levels above 10 require significant amounts of
memory to compress each block, so they are discouraged on
systems with less than 16&nbsp;GB of <acronym>RAM</acronym>.
<acronym>ZFS</acronym> also implements a selection of the
<acronym>Zstd</acronym> <emphasis>fast</emphasis> levels,
which get correspondingly faster but offer lower
compression ratios. <acronym>ZFS</acronym> supports
<literal>zstd-fast-1</literal> through
<literal>zstd-fast-10</literal>,
<literal>zstd-fast-20</literal> through
<literal>zstd-fast-100</literal> in increments of 10, and
finally <literal>zstd-fast-500</literal> and
pauamma_gundo.comUnsubmitted
Not Done
Inline Actions

That paragraph doesn't state how to change the compression from the default.

pauamma_gundo.com: That paragraph doesn't state how to change the compression from the default.
allanjudeAuthorUnsubmitted
Done
Inline Actions

That paragraph doesn't state how to change the compression from the default.

That is covered in the properties chapter, not sure if it makes sense to repeat it here. It might.

allanjude: > That paragraph doesn't state how to change the compression from the default. That is covered…
<literal>zstd-fast-1000</literal> which provide minimal
compression, but offer very high performance.</para>
<para>If ZFS is not able to allocate the required memory to
compress a block with <acronym>Zstd</acronym>, it will fall
back to storing the block uncompressed. This is unlikely
to happen outside of the highest levels of
<acronym>Zstd<acronym> on systems that are memory
constrained. The sysctl
<literal>kstat.zfs.misc.zstd.compress_alloc_fail</literal>
counts how many times this has occurred since the
<acronym>ZFS</acronym> module was loaded.</para>
</sect3>
</sect2> </sect2>
<sect2 xml:id="zfs-zfs-deduplication"> <sect2 xml:id="zfs-zfs-deduplication">
<title>Deduplication</title> <title>Deduplication</title>
<para>When enabled, <para>When enabled,
<link linkend="zfs-term-deduplication">deduplication</link> <link linkend="zfs-term-deduplication">deduplication</link>
uses the checksum of each block to detect duplicate blocks. uses the checksum of each block to detect duplicate blocks.
▲ Show 20 Lines • Show All 1,422 Lines • Show Last 20 Lines