.\" generated with Ronn/v0.7.3
.\" http://github.com/rtomayko/ronn/tree/0.7.3
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.TH "DMC" "1" "January 2018" "" ""
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.SH "NAME"
\fBdmc\fR \- controls the Disk Mount Conditioner
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.SH "SYNOPSIS"
\fBdmc start\fR \fImount\fR [\fIprofile\-name\fR|\fIprofile\-index\fR [\-boot]]
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.br
\fBdmc stop\fR \fImount\fR
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.br
\fBdmc status\fR \fImount\fR [\-json]
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.br
\fBdmc show\fR \fIprofile\-name\fR|\fIprofile\-index\fR
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.br
\fBdmc list\fR
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.br
\fBdmc select\fR \fImount\fR \fIprofile\-name\fR|\fIprofile\-index\fR
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.br
\fBdmc configure\fR \fImount\fR \fItype\fR \fIaccess\-time\fR \fIread\-throughput\fR \fIwrite\-throughput\fR [\fIioqueue\-depth\fR \fImaxreadcnt\fR \fImaxwritecnt\fR \fIsegreadcnt\fR \fIsegwritecnt\fR]
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.br
\fBdmc help | \-h\fR
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.br
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.SH "DESCRIPTION"
dmc(1) configures the Disk Mount Conditioner\. The Disk Mount Conditioner is a kernel provided service that can degrade the disk I/O being issued to specific mount points, providing the illusion that the I/O is executing on a slower device\. It can also cause the conditioned mount point to advertise itself as a different device type, e\.g\. the disk type of an SSD could be set to an HDD\. This behavior consequently changes various parameters such as read\-ahead settings, disk I/O throttling, etc\., which normally have different behavior depending on the underlying device type\.
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.SH "COMMANDS"
Common command parameters:
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.IP "\(bu" 4
\fImount\fR \- the mount point to be used in the command
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.IP "\(bu" 4
\fIprofile\-name\fR \- the name of a profile as shown in \fBdmc list\fR
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.IP "\(bu" 4
\fIprofile\-index\fR \- the index of a profile as shown in \fBdmc list\fR
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.IP "" 0
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.P
\fBdmc start\fR \fImount\fR [\fIprofile\-name\fR|\fIprofile\-index\fR [\-boot]]
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.br
\~\~\~\~Start the Disk Mount Conditioner on the given mount point with the current settings (from \fBdmc status\fR) or the given profile, if provided\. Optionally configure the profile to remain enabled across reboots, if \fI\-boot\fR is supplied\.
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.P
\fBdmc stop\fR \fImount\fR
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.br
\~\~\~\~Disable the Disk Mount Conditioner on the given mount point\. Also disables any settings that persist across reboot via the \fI\-boot\fR flag provided to \fBdmc start\fR, if any\.
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.P
\fBdmc status\fR \fImount\fR [\-json]
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.br
\~\~\~\~Display the current settings (including on/off state), optionally as JSON
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.P
\fBdmc show\fR \fIprofile\-name\fR|\fIprofile\-index\fR
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.br
\~\~\~\~Display the settings of the given profile
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.P
\fBdmc list\fR
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.br
\~\~\~\~Display all profile names and indices
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.P
\fBdmc select\fR \fImount\fR \fIprofile\-name\fR|\fIprofile\-index\fR
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.br
\~\~\~\~Choose a different profile for the given mount point without enabling or disabling the Disk Mount Conditioner
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.P
\fBdmc configure\fR \fImount\fR \fItype\fR \fIaccess\-time\fR \fIread\-throughput\fR \fIwrite\-throughput\fR [\fIioqueue\-depth\fR \fImaxreadcnt\fR \fImaxwritecnt\fR \fIsegreadcnt\fR \fIsegwritecnt\fR]
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.br
\~\~\~\~Select custom parameters for the given mount point rather than using the settings provided by a default profile\.
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.P
\~\~\~\~See \fBdmc list\fR for example parameter settings for various disk presets\.
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.IP "\(bu" 4
\fItype\fR \- \'SSD\' or \'HDD\'\. The type determines how various system behaviors like disk I/O throttling and read\-ahead algorithms affect the issued I/O\. Additionally, choosing \'HDD\' will attempt to simulate seek times, including drive spin\-up from idle\.
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.IP "\(bu" 4
\fIaccess\-time\fR \- latency in microseconds for a single I/O\. For SSD types this latency is applied exactly as specified to all I/O\. For HDD types, the latency scales based on a simulated seek time (thus making the access\-time the maximum latency or seek penalty)\.
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.IP "\(bu" 4
\fIread\-throughput\fR \- integer specifying megabytes\-per\-second maximum throughput for disk reads
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.IP "\(bu" 4
\fIwrite\-throughput\fR \- integer specifying megabytes\-per\-second maxmimu throughput for disk writes
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.IP "\(bu" 4
\fIioqueue\-depth\fR \- maximum number of commands that a device can accept
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.IP "\(bu" 4
\fImaxreadcnt\fR \- maximum byte count per read
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.IP "\(bu" 4
\fImaxwritecnt\fR \- maximum byte count per write
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.IP "\(bu" 4
\fIsegreadcnt\fR \- maximum physically disjoint segments processed per read
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.IP "\(bu" 4
\fIsegwritecnt\fR \- maximum physically disjoint segments processed per write
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.IP "" 0
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.P
\fBdmc help | \-h\fR
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.br
\~\~\~\~Display help text
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.SH "EXAMPLES"
\fBdmc start / \'5400 HDD\'\fR
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.P
\~\~\~\~Turn on the Disk Mount Conditioner for the boot volume, acting like a 5400 RPM hard drive\.
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.P
\fBdmc configure /Volumes/ExtDisk SSD 100 100 50\fR
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.P
\~\~\~\~Configure an external disk to use custom parameters to degrade performance as if it were a slow SSD with 100 microsecond latencies, 100MB/s read throughput, and 50MB/s write throughput\.
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.SH "IMPORTANT"
The Disk Mount Conditioner is not a \'simulator\'\. It can only degrade (or \'condition\') the I/O such that a faster disk device behaves like a slower device, not vice\-versa\. For example, a 5400 RPM hard drive cannot be conditioned to act like a SSD that is capable of a higher throughput than the theoretical limitations of the hard disk\.
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.P
In addition to running \fBdmc stop\fR, rebooting is also a sufficient way to clear any existing settings and disable Disk Mount Conditioner on all mount points (unless started with \fI\-boot\fR)\.
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.SH "SEE ALSO"
nlc(1)