diff options
authorNeilBrown <>2005-11-28 13:44:09 -0800
committerLinus Torvalds <>2005-11-28 14:42:25 -0800
commit22dfdf5212e5864b844f629736fb993d4611f190 (patch)
parent20c5ab6821b3a7aad31fb5a4660e9fe414fb37f6 (diff)
[PATCH] md: improve read speed to raid10 arrays using 'far copies'
raid10 has two different layouts. One uses near-copies (so multiple copies of a block are at the same or similar offsets of different devices) and the other uses far-copies (so multiple copies of a block are stored a greatly different offsets on different devices). The point of far-copies is that it allows the first section (normally first half) to be layed out in normal raid0 style, and thus provide raid0 sequential read performance. Unfortunately, the read balancing in raid10 makes some poor decisions for far-copies arrays and you don't get the desired performance. So turn off that bad bit of read_balance for far-copies arrays. With this patch, read speed of an 'f2' array is comparable with a raid0 with the same number of devices, though write speed is ofcourse still very slow. Signed-off-by: Neil Brown <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
1 files changed, 5 insertions, 1 deletions
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 867f06ae33d9..713dc9c2c730 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -552,7 +552,11 @@ static int read_balance(conf_t *conf, r10bio_t *r10_bio)
!test_bit(In_sync, &rdev->flags))
- if (!atomic_read(&rdev->nr_pending)) {
+ /* This optimisation is debatable, and completely destroys
+ * sequential read speed for 'far copies' arrays. So only
+ * keep it for 'near' arrays, and review those later.
+ */
+ if (conf->near_copies > 1 && !atomic_read(&rdev->nr_pending)) {
disk = ndisk;
slot = nslot;