svn commit: r320787 - head/sbin/newfs

[Warner Losh]

Author: imp
Date: Fri Jul  7 16:54:18 2017
New Revision: 320787
URL: https://svnweb.freebsd.org/changeset/base/320787

Log:
  Improve wording for -E and -t flags. -E never writes the entire disk,
  so don't imply that. Note that if BIO_DELETE isn't supported, the
  operation will fail (as opposed to writing the entire disk with
  zeros). Thin storage also benefits from trim. List more accurate
  reason why trim helps flash-memory.

Modified:
  head/sbin/newfs/newfs.8

Modified: head/sbin/newfs/newfs.8
==============================================================================
--- head/sbin/newfs/newfs.8	Fri Jul  7 16:25:58 2017	(r320786)
+++ head/sbin/newfs/newfs.8	Fri Jul  7 16:54:18 2017	(r320787)
@@ -79,11 +79,9 @@ The following options define the general layout polici
 .It Fl E
 Erase the content of the disk before making the filesystem.
 The reserved area in front of the superblock (for bootcode) will not be erased.
-.Pp
-This option is only relevant for flash based storage devices that use
-wear-leveling algorithms.
-.Pp
-Erasing may take a long time as it writes to every sector on the disk.
+Erasing is only relevant to flash-memory or thinly provisioned devices.
+Erasing may take a long time.
+If the device does not support BIO_DELETE, the command will fail.
 .It Fl J
 Enable journaling on the new file system via gjournal.
 See
@@ -264,9 +262,11 @@ Turn on the TRIM enable flag.
 If enabled, and if the underlying device supports the BIO_DELETE
 command, the file system will send a delete request to the underlying
 device for each freed block.
-The trim enable flag is typically set when the underlying device
-uses flash-memory as the device can use the delete command to
-pre-zero or at least avoid copying blocks that have been deleted.
+The trim enable flag is typically set for flash-memory devices to
+reduce write amplification which reduces wear on write-limited
+flash-memory and often improves long-term performance.
+Thinly provisioned storage also benefits by returning unused blocks to
+the global pool.
 .El
 .Pp
 The following options override the standard sizes for the disk geometry.