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Change target size of metaslabs from 256GB to 16GB

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= Old behavior

For vdev sizes 100GB to 50TB we keep ~200 metaslabs per
vdev and the metaslab size grows from 512MB to 256GB.
For vdev's bigger than that we start increasing the
number of metaslabs until we hit the 128K limit.

= New Behavior

For vdev sizes 100GB to 3TB we keep ~200 metaslabs per
vdev and the metaslab size grows from 512MB to 16GB.
For vdev's bigger than that we start increasing the
number of metaslabs until we hit the 128K limit.

= Reasoning

The old behavior makes metaslabs grow in size when
the vdev range is between 3TB (ms_size 16GB) and
32PB (ms_size 256GB). Even though keeping the number
of metaslabs is good in terms of potential number of
I/Os per TXG, these bigger metaslabs take longer
to be loaded and after they are loaded they can
take up a lot of memory because of their range trees.

This change tries to put a boundary in memory and
loading time for the specific range of vdev sizes.

Reviewed-by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Don Brady <don.brady@delphix.com>
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Closes #8324
This commit is contained in:
Serapheim Dimitropoulos
2019-01-25 16:38:27 -08:00
committed by Brian Behlendorf
parent df72b8bebe
commit c853f382db
3 changed files with 54 additions and 40 deletions
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man/man5/zfs-module-parameters.5
+2 -2
View File
@@ -320,7 +320,7 @@ Use \fB1\fR for yes (default) and \fB0\fR for no.
.sp
.ne 2
.na
\fBvdev_max_ms_count\fR (int)
\fBzfs_vdev_default_ms_count\fR (int)
.ad
.RS 12n
When a vdev is added target this number of metaslabs per top-level vdev.
@@ -331,7 +331,7 @@ Default value: \fB200\fR.
.sp
.ne 2
.na
\fBvdev_min_ms_count\fR (int)
\fBzfs_vdev_min_ms_count\fR (int)
.ad
.RS 12n
Minimum number of metaslabs to create in a top-level vdev.