sn_dmap(1) sn_dmap(1)
NAME
sn_dmap - Disk map utility
SYNOPSIS
sn_dmap [options] devname
DESCRIPTION
sn_dmap is a utility that can be used to manage disk volumes that are
thin-provisioned. Typically these volumes remap logical block address-
es (LBAs) and allocate space as needed. Space is allocated when a block
is first written and can only be freed by issuing a SCSI unmap command.
sn_dmap operates on one device at a time specified by the devname pa-
rameter. The devname parameter can either be a full path to the device
like /dev/mapper/mpathai or the StorNext volume label. By default
sn_dmap will print summary mapping information about the volume. More
detailed information may be displayed using the -v option.
OPTIONS
-? Display usage and exit.
-c Clear. Unmap all the blocks on the volume except the StorNext
label. This option should be used only to clean up a volume be-
fore a cvmkfs operation. This will effectively clear all the
blocks on the volume except the StorNext label and cannot be un-
done.
-C Clear. Unmap all the blocks on the volume including the
StorNext label. This option should be used only to clean up a
volume before a cvlabel and a cvmkfs operation. This will ef-
fectively clear all the blocks on the volume including the
StorNext label and cannot be undone.
-d[dddd]
Run in debug mode. The more "d's" specified, the more debug in-
formation is printed.
-f Force the clear or unmap operation without an warning message.
-h Help. Display usage and exit.
-l LBA The starting logical block address. Optional when the -v option
is sepcified and required for an unmap operation. See -u.
-n nblks
Specify the number of blocks. This option is required for an un-
map operation. See -u.
-o nsegments
Specify the number of segments to display. This option is valid
with the -v option and limits the number of segments displayed
to the specified value.
-u Unmap the range specified by the -l and -n options.
-v Verbose. Display information about all the segments. The -l
option can be specified to display segments starting with the
specified LBA. The -o may be specified to limit the output to
the specified number of segments.
-x Disply segment information in hexadecimal. This option is
available only with the -v option.
EXAMPLES
Display general mapping information about the given volume:
per1-# sn_dmap /dev/mapper/mpathal
/dev/mapper/mpathal {
segments blocks
mapped 4 2277376 1.09 GiBytes
unmapped 6 15818022912 7.37 TiBytes
total 10 15820300288 7.37 TiBytes
} snfs_meta_qx3_L23
Display verbose information about each segment of the given volume.
Note that we used the StorNext volume name as the device name in this
example:
per1-# sn_dmap -v snfs_meta_qx3_L23
/dev/mapper/mpathal {
Segment LBA NBlocks Status
0 0 8192 mapped 4.00 MiBytes
1 8192 7806976 unmapped 3.72 GiBytes
2 7815168 2088960 mapped 1020.00 MiBytes
3 9904128 5718016 unmapped 2.73 GiBytes
4 15622144 172032 mapped 84.00 MiBytes
5 15794176 4294959104 unmapped 2.00 TiBytes
6 4310753280 4294959104 unmapped 2.00 TiBytes
7 8605712384 4294959104 unmapped 2.00 TiBytes
8 12900671488 2919620608 unmapped 1.36 TiBytes
9 15820292096 8192 mapped 4.00 MiBytes
} snfs_meta_qx3_L23
Unmap a segment with the force option (no warning):
per1-# sn_dmap -f -u -l 7815168 -n 2088960 snfs_meta_qx3_L23
Verify that the segment is now unmapped:
per1-# sn_dmap -v snfs_meta_qx3_L23
/dev/mapper/mpathal {
Segment LBA NBlocks Status
0 0 8192 mapped 4.00 MiBytes
1 8192 15613952 unmapped 7.45 GiBytes
2 15622144 172032 mapped 84.00 MiBytes
3 15794176 4294959104 unmapped 2.00 TiBytes
4 4310753280 4294959104 unmapped 2.00 TiBytes
5 8605712384 4294959104 unmapped 2.00 TiBytes
6 12900671488 2919620608 unmapped 1.36 TiBytes
7 15820292096 8192 mapped 4.00 MiBytes
} snfs_meta_qx3_L23
Clear all mapped segments except those containing the StorNext label:
per1-# sn_dmap -c snfs_meta_qx3_L23
sn_dmap: *WARNING WARNING WARNING*
You are about to unmap all the blocks on the device /dev/mapper/mpathal.
This will destroy all data on the StorNext volume snfs_meta_qx3_L23
except the StorNext label. This operation can not be undone.
Do you want to procede? (y / n) -> y
Verify all is unmapped except the StorNext label (first and last seg-
ments):
per1-# sn_dmap -v snfs_meta_qx3_L23
/dev/mapper/mpathal {
Segment LBA NBlocks Status
0 0 8192 mapped 4.00 MiBytes
1 8192 4294959104 unmapped 2.00 TiBytes
2 4294967296 4294959104 unmapped 2.00 TiBytes
3 8589926400 4294959104 unmapped 2.00 TiBytes
4 12884885504 2935406592 unmapped 1.37 TiBytes
5 15820292096 8192 mapped 4.00 MiBytes
} snfs_meta_qx3_L23
NOTES
The unmap option (-u) is most likely useful only for development pur-
poses.
sn_dmap execs the cvlabel command (/usr/cvfs/bin/cvlabel) to match the
StorNext volume name to the device.
sn_dmap is currently supported only on Linux.
FILES
/System/Library/Filesystems/acfs.fs/Contents/bin/sn_dmap
SEE ALSO
cvlabel(8)
StorNext File System May 2015 sn_dmap(1)
Mac OS X 10.12.3 - Generated Sat Feb 4 18:16:48 CST 2017