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Add separate aggregation limit for non-rotating media

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Before sequential scrub patches ZFS never aggregated I/Os above 128KB.
Sequential scrub bumped that to 1MB, supposedly to reduce number of
head seeks for spinning disks.  But for SSDs it makes little to no
sense, especially on FreeBSD, where due to MAXPHYS limitation device
will likely still see bunch of 128KB I/Os instead of one large.
Having more strict aggregation limit for SSDs allows to avoid
allocation of large memory buffer and copy to/from it, that is a
serious problem when throughput reaches gigabytes per second.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Closes #8494
This commit is contained in:
Alexander Motin
2019-03-13 15:00:10 -04:00
committed by Brian Behlendorf
parent 12a935ee9c
commit 1af240f3b5
2 changed files with 21 additions and 1 deletions
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man/man5/zfs-module-parameters.5
+11
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@@ -2364,6 +2364,17 @@ Default value: \fB5\fR.
.RS 12n
Max vdev I/O aggregation size
.sp
Default value: \fB1,048,576\fR.
.RE
.sp
.ne 2
.na
\fBzfs_vdev_aggregation_limit_non_rotating\fR (int)
.ad
.RS 12n
Max vdev I/O aggregation size for non-rotating media
.sp
Default value: \fB131,072\fR.
.RE