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32 .\" @(#)newfs.8 8.6 (Berkeley) 5/3/95
33 .\" $FreeBSD: src/sbin/newfs/newfs.8,v 1.26.2.15 2003/05/13 12:16:08 joerg Exp $
41 .Nd construct a new UFS file system
46 .Op Fl S Ar sector-size
49 .Op Fl b Ar block-size
54 .Op Fl g Ar avgfilesize
58 .Op Fl l Ar interleave
59 .Op Fl m Ar free space
60 .Op Fl n Ar rotational positions
61 .Op Fl o Ar optimization
63 .Op Fl r Ar revolutions
75 .Op Fl b Ar block-size
81 .Op Fl m Ar free space
82 .Op Fl n Ar rotational positions
89 is used to initialize and clear filesystems before first use.
94 the disk must be labeled using
97 builds a file system on the specified special file.
98 (We often refer to the
102 although the special file need not be a physical disk.
103 In fact, it need not even be special.)
104 Typically the defaults are reasonable, however
106 has numerous options to allow the defaults to be selectively overridden.
109 is used to build a file system in virtual memory and then mount it
112 exits and the contents of the file system are lost
113 when the file system is unmounted.
116 is sent a signal while running,
117 for example during system shutdown,
118 it will attempt to unmount its
119 corresponding file system.
122 are the same as those to
126 flag is specified (see below), the special file is unused.
127 Otherwise, it is only used to read the disk label which provides
128 a set of configuration parameters for the memory based file system.
129 The special file is typically that of the primary swap area,
130 since that is where the file system will be backed up when
131 free memory gets low and the memory supporting
132 the file system has to be paged.
135 creates the raw character device
137 to represent the backing store while the mount is active. This device may
138 be read but not written and allows swap-based MFS filesystems to be dumped
141 The following options define the general layout policies:
142 .Bl -tag -width indent
144 For backward compatibility and for
147 Use TRIM to erase the device's data before creating the file system.
148 The underlying device must have the TRIM sysctl enabled.
149 Only devices that support TRIM will have such a sysctl option
150 .Va ( kern.cam.da.X.trim_enabled ) .
153 will use this file for the image of the filesystem. When
155 exits, this file will be left behind.
159 to copy the underlying filesystem into the MFS mount being created
162 Add a volume label to the new file system.
164 Cause the file system parameters to be printed out
165 without really creating the file system.
170 This options is primarily used to build root filesystems
171 that can be understood by older boot ROMs.
173 Use information for the specified disk from
175 instead of trying to get geometry information from the
178 Enables soft updates on the new filesystem.
179 .It Fl a Ar maxcontig
180 Specify the maximum number of contiguous blocks that will be
181 laid out before forcing a rotational delay (see the
184 The default value is 1.
187 for more details on how to set this option.
188 .It Fl b Ar block-size
189 The block size of the file system, in bytes. It must be a power of 2. The
190 default size is 16384 bytes, and the smallest allowable size is 4096 bytes.
191 The optimal block:fragment ratio is 8:1.
192 Other ratios are possible, but are not recommended,
193 and may produce unpredictable results.
194 .It Fl c Ar #cylinders/group
195 The number of cylinders per cylinder group in a file system. The default
196 is to compute the maximum allowed by the other parameters. This value is
197 dependent on a number of other parameters, in particular the block size
198 and the number of bytes per inode.
200 This parameter once specified the minimum time in milliseconds required to
201 initiate another disk transfer on the same cylinder. It was used in determining
202 the rotationally optimal layout for disk blocks within a file. Modern disks
203 with read/write-behind achieve higher performance with this feature disabled, so
204 this value should be left at the default value of 0 milliseconds. See
206 for more details on how to set this option.
208 Indicate the maximum number of blocks any single file can
209 allocate out of a cylinder group before it is forced to begin
210 allocating blocks from another cylinder group.
211 The default is about one quarter of the total blocks in a cylinder group.
214 for more details on how to set this option.
215 .It Fl f Ar frag-size
216 The fragment size of the file system in bytes. It must be a power of two
217 ranging in value between
221 The default is 2048 bytes.
222 .It Fl g Ar avgfilesize
223 The expected average file size for the file system.
225 The expected average number of files per directory on the file system.
226 .It Fl i Ar number of bytes per inode
227 Specify the density of inodes in the file system.
228 The default is to create an inode for every
231 If fewer inodes are desired, a larger number should be used;
232 to create more inodes a smaller number should be given.
233 One inode is required for each distinct file, so this value effectively
234 specifies the average file size on the file system.
235 .It Fl m Ar free space \&%
236 The percentage of space reserved from normal users; the minimum free
238 The default value used is
246 for more details on how to set this option.
247 .It Fl n Ar number of distinguished rotational positions
249 has the ability to keep track of the availability of blocks at different
250 rotational positions, so that it could lay out the data to be picked up with
251 minimum rotational latency. This parameter specifies the default number of
252 rotational positions to distinguish.
254 Nowadays this value should be set to 1 (which essentially disables the
255 rotational position table) because modern drives with read-ahead and
256 write-behind do better without the rotational position table.
257 .It Fl o Ar optimization\ preference
258 .Pq Cm space No or Cm time .
259 The file system can either be instructed to try to minimize the time spent
260 allocating blocks, or to try to minimize the space fragmentation on the disk.
261 If the value of minfree (see above) is less than 8%,
262 the default is to optimize for
264 if the value of minfree is greater than or equal to 8%,
265 the default is to optimize for
269 for more details on how to set this option.
271 The size of the file system in sectors. This value defaults to the size of the
272 raw partition specified in
276 will use the entire partition for the file system).
278 Specify that the disk does not contain any partitions, and that
280 should build a file system on the whole disk.
281 This option is useful for synthetic disks such as
283 It may also be used to allow
285 to operate on regular files.
286 When operating on a regular file,
288 will synthesize a reasonable geometry for the filesystem.
291 The following options override the standard sizes for the disk geometry.
292 Their default values are taken from the disk label.
293 Changing these defaults is useful only when using
295 to build a file system whose raw image will eventually be used on a
296 different type of disk than the one on which it is initially created
297 (for example on a write-once disk).
298 Note that changing any of these values from their defaults will make
301 to find the alternate superblocks if the standard superblock is lost.
302 .Bl -tag -width indent
303 .It Fl S Ar sector-size
304 The size of a sector in bytes (almost never anything but 512).
305 .It Fl k Ar sector \&0 skew , per track
306 Used to describe perturbations in the media format to compensate for
308 Track skew is the offset of sector 0 on track N relative to sector 0
309 on track N-1 on the same cylinder.
310 This option is of historical importance only; modern controllers are always fast
311 enough to handle operations back-to-back.
312 .It Fl l Ar hardware sector interleave
313 Used to describe perturbations in the media format to compensate for
315 Interleave is physical sector interleave on each track,
316 specified as the denominator of the ratio:
317 .Dl sectors read/sectors passed over
318 Thus an interleave of 1/1 implies contiguous layout, while 1/2 implies
319 logical sector 0 is separated by one sector from logical sector 1.
320 This option is of historical importance only; the physical sector layout of
321 modern disks is not visible from outside.
322 .It Fl p Ar spare sectors per track
323 Spare sectors (bad sector replacements) are physical sectors that occupy
324 space at the end of each track.
325 They are not counted as part of the sectors/track
327 since they are not available to the file system for data allocation.
328 This option is of historical importance only. Modern disks perform their own
329 bad sector allocation.
330 .It Fl r Ar revolutions/minute
331 The speed of the disk in revolutions per minute. This value is no longer of
332 interest, since all the parameters which depend on it are usually disabled.
333 .It Fl t Ar #tracks/cylinder
334 The number of tracks/cylinder available for data allocation by the file
337 If zero is specified, the value from the device geometry will be used.
338 .It Fl u Ar sectors/track
339 The number of sectors per track available for data allocation by the file
342 If zero is specified, the value from the device geometry will be used.
343 This does not include sectors reserved at the end of each track for bad
344 block replacement (see the
347 .It Fl x Ar spare sectors per cylinder
348 Spare sectors (bad sector replacements) are physical sectors that occupy
349 space at the end of the last track in the cylinder.
350 They are deducted from the sectors/track
352 of the last track of each cylinder since they are not available to the file
353 system for data allocation.
354 This option is of historical importance only. Modern disks perform their own
355 bad sector allocation.
360 command are as described for the
362 command, except for the
366 That option is as follows:
367 .Bl -tag -width indent
369 Options are specified with a
371 flag followed by a comma separated string of options.
374 man page for possible options and their meanings.
377 .Dl newfs /dev/ad3s1a
384 will use a block size of 16384 bytes, a fragment size of 2048 bytes
385 and the largest possible number of cylinders per group.
386 These values tend to produce better performance for most applications
387 than the historical defaults
388 (8192 byte block size and 1024 byte fragment size).
389 This large fragment size
390 may lead to large amounts of wasted space
391 on filesystems that contain a large number of small files.
393 .Dl mount_mfs -s 131072 -o nosuid,nodev,nosymfollow /dev/da0s1b /tmp
395 Mount a 64 MB large memory file system on
421 .%T A Fast File System for UNIX
422 .%J ACM Transactions on Computer Systems 2
426 .%O (reprinted in the BSD System Manager's Manual)