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authorKeld Simonsen <keld@dkuug.dk>2008-03-04 14:29:34 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-03-04 16:35:18 -0800
commit8ed3a19563b6c05b7625649b1769ddb063d53253 (patch)
treead774e5920efc4c9bcf751ad31061cefe81faf35
parent27c529bb8e906d5d692152bc127cc09477d3629e (diff)
downloadkernel-8ed3a19563b6c05b7625649b1769ddb063d53253.tar.gz
md: don't attempt read-balancing for raid10 'far' layouts
This patch changes the disk to be read for layout "far > 1" to always be the disk with the lowest block address. Thus the chunks to be read will always be (for a fully functioning array) from the first band of stripes, and the raid will then work as a raid0 consisting of the first band of stripes. Some advantages: The fastest part which is the outer sectors of the disks involved will be used. The outer blocks of a disk may be as much as 100 % faster than the inner blocks. Average seek time will be smaller, as seeks will always be confined to the first part of the disks. Mixed disks with different performance characteristics will work better, as they will work as raid0, the sequential read rate will be number of disks involved times the IO rate of the slowest disk. If a disk is malfunctioning, the first disk which is working, and has the lowest block address for the logical block will be used. Signed-off-by: Keld Simonsen <keld@dkuug.dk> Signed-off-by: Neil Brown <neilb@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--drivers/md/raid10.c12
1 files changed, 9 insertions, 3 deletions
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 5de42d87bf4e..6c486d839c99 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -537,7 +537,8 @@ static int read_balance(conf_t *conf, r10bio_t *r10_bio)
current_distance = abs(r10_bio->devs[slot].addr -
conf->mirrors[disk].head_position);
- /* Find the disk whose head is closest */
+ /* Find the disk whose head is closest,
+ * or - for far > 1 - find the closest to partition beginning */
for (nslot = slot; nslot < conf->copies; nslot++) {
int ndisk = r10_bio->devs[nslot].devnum;
@@ -557,8 +558,13 @@ static int read_balance(conf_t *conf, r10bio_t *r10_bio)
slot = nslot;
break;
}
- new_distance = abs(r10_bio->devs[nslot].addr -
- conf->mirrors[ndisk].head_position);
+
+ /* for far > 1 always use the lowest address */
+ if (conf->far_copies > 1)
+ new_distance = r10_bio->devs[nslot].addr;
+ else
+ new_distance = abs(r10_bio->devs[nslot].addr -
+ conf->mirrors[ndisk].head_position);
if (new_distance < current_distance) {
current_distance = new_distance;
disk = ndisk;