From 40c9a66a5c1a89d621daa2184888e66952b06a71 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Thu, 4 Oct 2012 16:34:21 +1000 Subject: Add --data-offset flag for Create and Grow This can be used to over-ride the automatic assignment of data offset. For --create, it is useful to re-create old arrays where different defaults applied. For --grow it may be able to force a reshape in the reverse direction. Signed-off-by: NeilBrown --- mdadm.8.in | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) (limited to 'mdadm.8.in') diff --git a/mdadm.8.in b/mdadm.8.in index 845c00cd..255b6505 100644 --- a/mdadm.8.in +++ b/mdadm.8.in @@ -767,6 +767,34 @@ or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES. The file must be stored on a separate device, not on the RAID array being reshaped. +.TP +.B \-\-data\-offset= +Arrays with 1.x metadata can leave a gap between the start of the +device and the start of array data. This gap can be used for various +metadata. The start of data is known as the +.IR data\-offset . +Normally an appropriate data offset is computed automatically. +However it can be useful to set it explicitly such as when re-creating +an array which was originally created using a different version of +.I mdadm +which computed a different offset. + +Setting the offset explicitly over-rides the default. The value given +is in Kilobytes unless an 'M' or 'G' suffix is given. + +Since Linux 3.4, +.B \-\-data\-offset +can also be used with +.B --grow +for some RAID levels (initially on RAID10). This allows the +data-offset to be changed as part of the reshape process. When the +data offset is changed, no backup file is required as the difference +in offsets is used to provide the same functionality. + +When the new offset is earlier than the old offset, the number of +devices in the array cannot shrink. When it is after the old offset, +the number of devices in the array cannot increase. + .TP .BR \-\-continue This option is complementary to the -- cgit v1.2.3