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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 file system
45 .Op Fl S Ar sector-size
48 .Op Fl b Ar block-size
53 .Op Fl g Ar avgfilesize
57 .Op Fl l Ar interleave
58 .Op Fl m Ar free space
59 .Op Fl n Ar rotational positions
60 .Op Fl o Ar optimization
62 .Op Fl r Ar revolutions
74 .Op Fl b Ar block-size
80 .Op Fl m Ar free space
81 .Op Fl n Ar rotational positions
88 is used to initialize and clear filesystems before first use.
93 the disk must be labeled using
96 builds a file system on the specified special file.
97 (We often refer to the
101 although the special file need not be a physical disk.
102 In fact, it need not even be special.)
103 Typically the defaults are reasonable, however
105 has numerous options to allow the defaults to be selectively overridden.
108 is used to build a file system in virtual memory and then mount it
111 exits and the contents of the file system are lost
112 when the file system is unmounted.
115 is sent a signal while running,
116 for example during system shutdown,
117 it will attempt to unmount its
118 corresponding file system.
121 are the same as those to
125 flag is specified (see below), the special file is unused.
126 Otherwise, it is only used to read the disk label which provides
127 a set of configuration parameters for the memory based file system.
128 The special file is typically that of the primary swap area,
129 since that is where the file system will be backed up when
130 free memory gets low and the memory supporting
131 the file system has to be paged.
133 The following options define the general layout policies:
134 .Bl -tag -width indent
136 For backward compatibility and for
140 will use this file for the image of the filesystem. When
142 exits, this file will be left behind.
144 Cause the file system parameters to be printed out
145 without really creating the file system.
150 This options is primarily used to build root filesystems
151 that can be understood by older boot ROMs.
153 Use information for the specified disk from
155 instead of trying to get the information from a disklabel.
157 Enables soft updates on the new filesystem.
158 .It Fl a Ar maxcontig
159 Specify the maximum number of contiguous blocks that will be
160 laid out before forcing a rotational delay (see the
163 The default value is 1.
166 for more details on how to set this option.
167 .It Fl b Ar block-size
168 The block size of the file system, in bytes. It must be a power of 2. The
169 default size is 16384 bytes, and the smallest allowable size is 4096 bytes.
170 The optimal block:fragment ratio is 8:1.
171 Other ratios are possible, but are not recommended,
172 and may produce unpredictable results.
173 .It Fl c Ar #cylinders/group
174 The number of cylinders per cylinder group in a file system. The default
175 is to compute the maximum allowed by the other parameters. This value is
176 dependent on a number of other parameters, in particular the block size
177 and the number of bytes per inode.
179 This parameter once specified the minimum time in milliseconds required to
180 initiate another disk transfer on the same cylinder. It was used in determining
181 the rotationally optimal layout for disk blocks within a file. Modern disks
182 with read/write-behind achieve higher performance with this feature disabled, so
183 this value should be left at the default value of 0 milliseconds. See
185 for more details on how to set this option.
187 Indicate the maximum number of blocks any single file can
188 allocate out of a cylinder group before it is forced to begin
189 allocating blocks from another cylinder group.
190 The default is about one quarter of the total blocks in a cylinder group.
193 for more details on how to set this option.
194 .It Fl f Ar frag-size
195 The fragment size of the file system in bytes. It must be a power of two
196 ranging in value between
200 The default is 2048 bytes.
201 .It Fl g Ar avgfilesize
202 The expected average file size for the file system.
204 The expected average number of files per directory on the file system.
205 .It Fl i Ar number of bytes per inode
206 Specify the density of inodes in the file system.
207 The default is to create an inode for every
210 If fewer inodes are desired, a larger number should be used;
211 to create more inodes a smaller number should be given.
212 One inode is required for each distinct file, so this value effectively
213 specifies the average file size on the file system.
214 .It Fl m Ar free space \&%
215 The percentage of space reserved from normal users; the minimum free
217 The default value used is
221 .Aq Pa ufs/ffs/fs.h ,
225 for more details on how to set this option.
226 .It Fl n Ar number of distinguished rotational positions
227 UFS has the ability to keep track of the availability of blocks at different
228 rotational positions, so that it could lay out the data to be picked up with
229 minimum rotational latency. This parameter specifies the default number of
230 rotational positions to distinguish.
232 Nowadays this value should be set to 1 (which essentially disables the
233 rotational position table) because modern drives with read-ahead and
234 write-behind do better without the rotational position table.
235 .It Fl o Ar optimization\ preference
236 .Pq Ar space No or Ar time .
237 The file system can either be instructed to try to minimize the time spent
238 allocating blocks, or to try to minimize the space fragmentation on the disk.
239 If the value of minfree (see above) is less than 8%,
240 the default is to optimize for
242 if the value of minfree is greater than or equal to 8%,
243 the default is to optimize for
247 for more details on how to set this option.
249 The size of the file system in sectors. This value defaults to the size of the
250 raw partition specified in
254 will use the entire partition for the file system).
256 Specify that the disk does not contain any partitions, and that
258 should build a file system on the whole disk.
259 This option is useful for synthetic disks such as
263 The following options override the standard sizes for the disk geometry.
264 Their default values are taken from the disk label.
265 Changing these defaults is useful only when using
267 to build a file system whose raw image will eventually be used on a
268 different type of disk than the one on which it is initially created
269 (for example on a write-once disk).
270 Note that changing any of these values from their defaults will make
273 to find the alternate superblocks if the standard superblock is lost.
274 .Bl -tag -width indent
275 .It Fl S Ar sector-size
276 The size of a sector in bytes (almost never anything but 512).
277 .It Fl k Ar sector \&0 skew , per track
278 Used to describe perturbations in the media format to compensate for
280 Track skew is the offset of sector 0 on track N relative to sector 0
281 on track N-1 on the same cylinder.
282 This option is of historical importance only; modern controllers are always fast
283 enough to handle operations back-to-back.
284 .It Fl l Ar hardware sector interleave
285 Used to describe perturbations in the media format to compensate for
287 Interleave is physical sector interleave on each track,
288 specified as the denominator of the ratio:
289 .Dl sectors read/sectors passed over
290 Thus an interleave of 1/1 implies contiguous layout, while 1/2 implies
291 logical sector 0 is separated by one sector from logical sector 1.
292 This option is of historical importance only; the physical sector layout of
293 modern disks is not visible from outside.
294 .It Fl p Ar spare sectors per track
295 Spare sectors (bad sector replacements) are physical sectors that occupy
296 space at the end of each track.
297 They are not counted as part of the sectors/track
299 since they are not available to the file system for data allocation.
300 This option is of historical importance only. Modern disks perform their own
301 bad sector allocation.
302 .It Fl r Ar revolutions/minute
303 The speed of the disk in revolutions per minute. This value is no longer of
304 interest, since all the parameters which depend on it are usually disabled.
305 .It Fl t Ar #tracks/cylinder
306 The number of tracks/cylinder available for data allocation by the file
309 If zero is specified, the value from the disklabel will be used.
310 .It Fl u Ar sectors/track
311 The number of sectors per track available for data allocation by the file
314 If zero is specified, the value from the disklabel will be used.
315 This does not include sectors reserved at the end of each track for bad
316 block replacement (see the
319 .It Fl x Ar spare sectors per cylinder
320 Spare sectors (bad sector replacements) are physical sectors that occupy
321 space at the end of the last track in the cylinder.
322 They are deducted from the sectors/track
324 of the last track of each cylinder since they are not available to the file
325 system for data allocation.
326 This option is of historical importance only. Modern disks perform their own
327 bad sector allocation.
332 command are as described for the
334 command, except for the
338 That option is as follows:
339 .Bl -tag -width indent
341 Options are specified with a
343 flag followed by a comma separated string of options.
346 man page for possible options and their meanings.
349 .Dl newfs /dev/ad3s1a
351 Creates a new ufs file system on
354 will use a block size of 16384 bytes, a fragment size of 2048 bytes
355 and the largest possible number of cylinders per group.
356 These values tend to produce better performance for most applications
357 than the historical defaults
358 (8192 byte block size and 1024 byte fragment size).
359 This large fragment size
360 may lead to large amounts of wasted space
361 on filesystems that contain a large number of small files.
363 .Dl mount_mfs -s 131072 -o nosuid,nodev,nosymfollow /dev/da0s1b /tmp
365 Mount a 64 MB large memory file system on
391 .%T A Fast File System for UNIX
392 .%J ACM Transactions on Computer Systems 2
396 .%O (reprinted in the BSD System Manager's Manual)