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[PATCH] md: add write-intent-bitmap support to raid5

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Most awkward part of this is delaying write requests until bitmap updates have
been flushed.

To achieve this, we have a sequence number (seq_flush) which is incremented
each time the raid5 is unplugged.

If the raid thread notices that this has changed, it flushes bitmap changes,
and assigned the value of seq_flush to seq_write.

When a write request arrives, it is given the number from seq_write, and that
write request may not complete until seq_flush is larger than the saved seq
number.

We have a new queue for storing stripes which are waiting for a bitmap flush
and an extra flag for stripes to record if the write was 'degraded' and so
should not clear the a bit in the bitmap.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
NeilBrown
2005-09-09 16:23:54 -07:00
committed by Linus Torvalds
parent 0002b2718d
commit 72626685dc
3 changed files with 137 additions and 13 deletions
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3
drivers/md/md.c
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@@ -645,7 +645,7 @@ static int super_90_validate(mddev_t *mddev, mdk_rdev_t *rdev)
if (sb->state & (1<<MD_SB_BITMAP_PRESENT) &&
mddev->bitmap_file == NULL) {
if (mddev->level != 1) {
if (mddev->level != 1 && mddev->level != 5) {
/* FIXME use a better test */
printk(KERN_WARNING "md: bitmaps only support for raid1\n");
return -EINVAL;
@@ -3517,7 +3517,6 @@ void md_done_sync(mddev_t *mddev, int blocks, int ok)
*/
void md_write_start(mddev_t *mddev, struct bio *bi)
{
DEFINE_WAIT(w);
if (bio_data_dir(bi) != WRITE)
return;