From ece5cff0da9e696c360fff592cb5f51b6419e4d6 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Mon, 14 Dec 2009 12:49:56 +1100 Subject: md: Support write-intent bitmaps with externally managed metadata. In this case, the metadata needs to not be in the same sector as the bitmap. md will not read/write any bitmap metadata. Config must be done via sysfs and when a recovery makes the array non-degraded again, writing 'true' to 'bitmap/can_clear' will allow bits in the bitmap to be cleared again. Signed-off-by: NeilBrown --- Documentation/md.txt | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'Documentation/md.txt') diff --git a/Documentation/md.txt b/Documentation/md.txt index 18fad687622..21d26fb5d02 100644 --- a/Documentation/md.txt +++ b/Documentation/md.txt @@ -322,6 +322,22 @@ All md devices contain: 'backlog' sets a limit on the number of concurrent background writes. If there are more than this, new writes will by synchronous. + bitmap/metadata + This can be either 'internal' or 'external'. + 'internal' is the default and means the metadata for the bitmap + is stored in the first 256 bytes of the allocated space and is + managed by the md module. + 'external' means that bitmap metadata is managed externally to + the kernel (i.e. by some userspace program) + bitmap/can_clear + This is either 'true' or 'false'. If 'true', then bits in the + bitmap will be cleared when the corresponding blocks are thought + to be in-sync. If 'false', bits will never be cleared. + This is automatically set to 'false' if a write happens on a + degraded array, or if the array becomes degraded during a write. + When metadata is managed externally, it should be set to true + once the array becomes non-degraded, and this fact has been + recorded in the metadata. -- cgit v1.2.2