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NEWFS(8) FreeBSD System Manager's Manual NEWFS(8)
NAME
newfs, mount_mfs -- construct a new file system
SYNOPSIS
newfs [-NOU] [-S sector-size] [-T disktype] [-a maxcontig]
[-b block-size] [-c cylinders] [-d rotdelay] [-e maxbpg]
[-f frag-size] [-g avgfilesize] [-h avfpdir] [-i bytes] [-k skew]
[-l interleave] [-m free space] [-n rotational positions]
[-o optimization] [-p sectors] [-r revolutions] [-s size]
[-t tracks] [-u sectors] [-v] [-x sectors] special
mount_mfs [-NU] [-F file] [-T disktype] [-a maxcontig] [-b block-size]
[-c cylinders] [-d rotdelay] [-e maxbpg] [-f frag-size] [-i bytes]
[-m free space] [-n rotational positions] [-o options] [-s size]
[-v] special node
DESCRIPTION
Newfs is used to initialize and clear filesystems before first use.
Before running newfs or mount_mfs, the disk must be labeled using
disklabel(8). Newfs builds a file system on the specified special file.
(We often refer to the ``special file'' as the ``disk'', although the
special file need not be a physical disk. In fact, it need not even be
special.) Typically the defaults are reasonable, however newfs has
numerous options to allow the defaults to be selectively overridden.
Mount_mfs is used to build a file system in virtual memory and then mount
it on a specified node. Mount_mfs exits and the contents of the file
system are lost when the file system is unmounted. If mount_mfs is sent
a signal while running, for example during system shutdown, it will
attempt to unmount its corresponding file system. The parameters to
mount_mfs are the same as those to newfs. If the -T flag is specified
(see below), the special file is unused. Otherwise, it is only used to
read the disk label which provides a set of configuration parameters for
the memory based file system. The special file is typically that of the
primary swap area, since that is where the file system will be backed up
when free memory gets low and the memory supporting the file system has
to be paged.
The following options define the general layout policies:
-T disktype
For backward compatibility and for mount_mfs.
-F file
Mount_mfs will use this file for the image of the filesystem.
When mount_mfs exits, this file will be left behind.
-N Cause the file system parameters to be printed out without really
creating the file system.
-O Create a 4.3BSD format filesystem. This options is primarily
used to build root filesystems that can be understood by older
boot ROMs.
-T Use information for the specified disk from /etc/disktab instead
of trying to get the information from a disklabel.
-U Enables soft updates on the new filesystem.
-a maxcontig
Specify the maximum number of contiguous blocks that will be laid
out before forcing a rotational delay (see the -d option). The
default value is 1. See tunefs(8) for more details on how to set
this option.
-b block-size
The block size of the file system, in bytes. It must be a power
of 2. The default size is 16384 bytes, and the smallest allow-
able size is 4096 bytes. The optimal block:fragment ratio is
8:1. Other ratios are possible, but are not recommended, and may
produce unpredictable results.
-c #cylinders/group
The number of cylinders per cylinder group in a file system. The
default is to compute the maximum allowed by the other parame-
ters. This value is dependent on a number of other parameters,
in particular the block size and the number of bytes per inode.
-d rotdelay
This parameter once specified the minimum time in milliseconds
required to initiate another disk transfer on the same cylinder.
It was used in determining the rotationally optimal layout for
disk blocks within a file. Modern disks with read/write-behind
achieve higher performance with this feature disabled, so this
value should be left at the default value of 0 milliseconds. See
tunefs(8) for more details on how to set this option.
-e maxbpg
Indicate the maximum number of blocks any single file can allo-
cate out of a cylinder group before it is forced to begin allo-
cating blocks from another cylinder group. The default is about
one quarter of the total blocks in a cylinder group. See
tunefs(8) for more details on how to set this option.
-f frag-size
The fragment size of the file system in bytes. It must be a
power of two ranging in value between blocksize/8 and blocksize.
The default is 2048 bytes.
-g avgfilesize
The expected average file size for the file system.
-h avgfpdir
The expected average number of files per directory on the file
system.
-i number of bytes per inode
Specify the density of inodes in the file system. The default is
to create an inode for every (4 * frag-size) bytes of data space.
If fewer inodes are desired, a larger number should be used; to
create more inodes a smaller number should be given. One inode
is required for each distinct file, so this value effectively
specifies the average file size on the file system.
-m free space %
The percentage of space reserved from normal users; the minimum
free space threshold. The default value used is defined by
MINFREE from <ufs/ffs/fs.h>, currently 8%. See tunefs(8) for
more details on how to set this option.
-n number of distinguished rotational positions
UFS has the ability to keep track of the availability of blocks
at different rotational positions, so that it could lay out the
data to be picked up with minimum rotational latency. This
parameter specifies the default number of rotational positions to
distinguish.
Nowadays this value should be set to 1 (which essentially dis-
ables the rotational position table) because modern drives with
read-ahead and write-behind do better without the rotational
position table.
-o optimization preference
(space or time). The file system can either be instructed to try
to minimize the time spent allocating blocks, or to try to mini-
mize the space fragmentation on the disk. If the value of min-
free (see above) is less than 8%, the default is to optimize for
space; if the value of minfree is greater than or equal to 8%,
the default is to optimize for time. See tunefs(8) for more
details on how to set this option.
-s size
The size of the file system in sectors. This value defaults to
the size of the raw partition specified in special (in other
words, newfs will use the entire partition for the file system).
-v Specify that the disk does not contain any partitions, and that
newfs should build a file system on the whole disk. This option
is useful for synthetic disks such as vinum.
The following options override the standard sizes for the disk geometry.
Their default values are taken from the disk label. Changing these
defaults is useful only when using newfs to build a file system whose raw
image will eventually be used on a different type of disk than the one on
which it is initially created (for example on a write-once disk). Note
that changing any of these values from their defaults will make it impos-
sible for fsck(8) to find the alternate superblocks if the standard
superblock is lost.
-S sector-size
The size of a sector in bytes (almost never anything but 512).
-k sector 0 skew, per track
Used to describe perturbations in the media format to compensate
for a slow controller. Track skew is the offset of sector 0 on
track N relative to sector 0 on track N-1 on the same cylinder.
This option is of historical importance only; modern controllers
are always fast enough to handle operations back-to-back.
-l hardware sector interleave
Used to describe perturbations in the media format to compensate
for a slow controller. Interleave is physical sector interleave
on each track, specified as the denominator of the ratio:
sectors read/sectors passed over
Thus an interleave of 1/1 implies contiguous layout, while 1/2
implies logical sector 0 is separated by one sector from logical
sector 1. This option is of historical importance only; the
physical sector layout of modern disks is not visible from out-
side.
-p spare sectors per track
Spare sectors (bad sector replacements) are physical sectors that
occupy space at the end of each track. They are not counted as
part of the sectors/track (-u) since they are not available to
the file system for data allocation. This option is of histori-
cal importance only. Modern disks perform their own bad sector
allocation.
-r revolutions/minute
The speed of the disk in revolutions per minute. This value is
no longer of interest, since all the parameters which depend on
it are usually disabled.
-t #tracks/cylinder
The number of tracks/cylinder available for data allocation by
the file system. The default is 1. If zero is specified, the
value from the disklabel will be used.
-u sectors/track
The number of sectors per track available for data allocation by
the file system. The default is 4096. If zero is specified, the
value from the disklabel will be used. This does not include
sectors reserved at the end of each track for bad block replace-
ment (see the -p option).
-x spare sectors per cylinder
Spare sectors (bad sector replacements) are physical sectors that
occupy space at the end of the last track in the cylinder. They
are deducted from the sectors/track (-u) of the last track of
each cylinder since they are not available to the file system for
data allocation. This option is of historical importance only.
Modern disks perform their own bad sector allocation.
The options to the mount_mfs command are as described for the newfs com-
mand, except for the -o option.
That option is as follows:
-o Options are specified with a -o flag followed by a comma sepa-
rated string of options. See the mount(8) man page for possible
options and their meanings.
EXAMPLES
newfs /dev/ad3s1a
Creates a new ufs file system on ad3s1a. newfs will use a block size of
16384 bytes, a fragment size of 2048 bytes and the largest possible num-
ber of cylinders per group. These values tend to produce better perfor-
mance for most applications than the historical defaults (8192 byte block
size and 1024 byte fragment size). This large fragment size may lead to
large amounts of wasted space on filesystems that contain a large number
of small files.
mount_mfs -s 131072 -o nosuid,nodev,nosymfollow /dev/da0s1b /tmp
Mount a 64 MB large memory file system on /tmp, with mount(8) options
nosuid, nodev, and nosymfollow.
SEE ALSO
fdformat(1), disktab(5), fs(5), camcontrol(8), disklabel(8), diskpart(8),
dumpfs(8), fsck(8), mount(8), tunefs(8), vinum(8)
M. McKusick, W. Joy, S. Leffler, and R. Fabry, "A Fast File System for
UNIX", ACM Transactions on Computer Systems 2, 3, pp 181-197, August
1984, (reprinted in the BSD System Manager's Manual).
HISTORY
The newfs command appeared in 4.2BSD.
FreeBSD 4.9 May 13, 2003 FreeBSD 4.9
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