From: NeilBrown This allows a device in a raid1 to be marked as "write mostly". Read requests will only be sent if there is no other option. Signed-off-by: Neil Brown Signed-off-by: Andrew Morton --- drivers/md/md.c | 18 ++++++++++ drivers/md/raid1.c | 76 +++++++++++++++++++++++++++++++--------------- include/linux/raid/md_k.h | 3 + include/linux/raid/md_p.h | 11 +++++- 4 files changed, 82 insertions(+), 26 deletions(-) diff -puN drivers/md/md.c~md-support-write-mostly-device-in-raid1 drivers/md/md.c --- 25/drivers/md/md.c~md-support-write-mostly-device-in-raid1 Wed Aug 17 13:39:23 2005 +++ 25-akpm/drivers/md/md.c Wed Aug 17 13:39:23 2005 @@ -671,6 +671,7 @@ static int super_90_validate(mddev_t *md if (mddev->level != LEVEL_MULTIPATH) { rdev->faulty = 0; + rdev->flags = 0; desc = sb->disks + rdev->desc_nr; if (desc->state & (1<in_sync = 1; rdev->raid_disk = desc->raid_disk; } + if (desc->state & (1<flags); } else /* MULTIPATH are always insync */ rdev->in_sync = 1; return 0; @@ -778,6 +781,8 @@ static void super_90_sync(mddev_t *mddev spare++; working++; } + if (test_bit(WriteMostly, &rdev2->flags)) + d->state |= (1<raid_disk = role; break; } + rdev->flags = 0; + if (sb->devflags & WriteMostly1) + set_bit(WriteMostly, &rdev->flags); } else /* MULTIPATH are always insync */ rdev->in_sync = 1; @@ -2151,6 +2159,8 @@ static int get_disk_info(mddev_t * mddev info.state |= (1<flags)) + info.state |= (1<saved_raid_disk = rdev->raid_disk; rdev->in_sync = 0; /* just to be sure */ + if (info->state & (1<flags); + rdev->raid_disk = -1; err = bind_rdev_to_array(rdev, mddev); if (err) @@ -2277,6 +2290,9 @@ static int add_new_disk(mddev_t * mddev, else rdev->in_sync = 0; + if (info->state & (1<flags); + err = bind_rdev_to_array(rdev, mddev); if (err) { export_rdev(rdev); @@ -3329,6 +3345,8 @@ static int md_seq_show(struct seq_file * char b[BDEVNAME_SIZE]; seq_printf(seq, " %s[%d]", bdevname(rdev->bdev,b), rdev->desc_nr); + if (test_bit(WriteMostly, &rdev->flags)) + seq_printf(seq, "(W)"); if (rdev->faulty) { seq_printf(seq, "(F)"); continue; diff -puN drivers/md/raid1.c~md-support-write-mostly-device-in-raid1 drivers/md/raid1.c --- 25/drivers/md/raid1.c~md-support-write-mostly-device-in-raid1 Wed Aug 17 13:39:23 2005 +++ 25-akpm/drivers/md/raid1.c Wed Aug 17 13:39:23 2005 @@ -360,13 +360,14 @@ static int read_balance(conf_t *conf, r1 { const unsigned long this_sector = r1_bio->sector; int new_disk = conf->last_used, disk = new_disk; + int wonly_disk = -1; const int sectors = r1_bio->sectors; sector_t new_distance, current_distance; - mdk_rdev_t *new_rdev, *rdev; + mdk_rdev_t *rdev; rcu_read_lock(); /* - * Check if it if we can balance. We can balance on the whole + * Check if we can balance. We can balance on the whole * device if no resync is going on, or below the resync window. * We take the first readable disk when above the resync window. */ @@ -376,11 +377,16 @@ static int read_balance(conf_t *conf, r1 /* Choose the first operation device, for consistancy */ new_disk = 0; - while ((new_rdev=conf->mirrors[new_disk].rdev) == NULL || - !new_rdev->in_sync) { - new_disk++; - if (new_disk == conf->raid_disks) { - new_disk = -1; + for (rdev = conf->mirrors[new_disk].rdev; + !rdev || !rdev->in_sync + || test_bit(WriteMostly, &rdev->flags); + rdev = conf->mirrors[++new_disk].rdev) { + + if (rdev && rdev->in_sync) + wonly_disk = new_disk; + + if (new_disk == conf->raid_disks - 1) { + new_disk = wonly_disk; break; } } @@ -389,16 +395,26 @@ static int read_balance(conf_t *conf, r1 /* make sure the disk is operational */ - while ((new_rdev=conf->mirrors[new_disk].rdev) == NULL || - !new_rdev->in_sync) { + for (rdev = conf->mirrors[new_disk].rdev; + !rdev || !rdev->in_sync || + test_bit(WriteMostly, &rdev->flags); + rdev = conf->mirrors[new_disk].rdev) { + + if (rdev && rdev->in_sync) + wonly_disk = new_disk; + if (new_disk <= 0) new_disk = conf->raid_disks; new_disk--; if (new_disk == disk) { - new_disk = -1; - goto rb_out; + new_disk = wonly_disk; + break; } } + + if (new_disk < 0) + goto rb_out; + disk = new_disk; /* now disk == new_disk == starting point for search */ @@ -419,37 +435,41 @@ static int read_balance(conf_t *conf, r1 disk = conf->raid_disks; disk--; - if ((rdev=conf->mirrors[disk].rdev) == NULL || - !rdev->in_sync) + rdev = conf->mirrors[disk].rdev; + + if (!rdev || + !rdev->in_sync || + test_bit(WriteMostly, &rdev->flags)) continue; if (!atomic_read(&rdev->nr_pending)) { new_disk = disk; - new_rdev = rdev; break; } new_distance = abs(this_sector - conf->mirrors[disk].head_position); if (new_distance < current_distance) { current_distance = new_distance; new_disk = disk; - new_rdev = rdev; } } while (disk != conf->last_used); -rb_out: + rb_out: if (new_disk >= 0) { - conf->next_seq_sect = this_sector + sectors; - conf->last_used = new_disk; - atomic_inc(&new_rdev->nr_pending); - if (!new_rdev->in_sync) { + rdev = conf->mirrors[new_disk].rdev; + if (!rdev) + goto retry; + atomic_inc(&rdev->nr_pending); + if (!rdev->in_sync) { /* cannot risk returning a device that failed * before we inc'ed nr_pending */ - atomic_dec(&new_rdev->nr_pending); + atomic_dec(&rdev->nr_pending); goto retry; } + conf->next_seq_sect = this_sector + sectors; + conf->last_used = new_disk; } rcu_read_unlock(); @@ -1109,6 +1129,7 @@ static sector_t sync_request(mddev_t *md sector_t max_sector, nr_sectors; int disk; int i; + int wonly; int write_targets = 0; int sync_blocks; int still_degraded = 0; @@ -1164,14 +1185,21 @@ static sector_t sync_request(mddev_t *md */ disk = conf->last_used; /* make sure disk is operational */ - + wonly = disk; while (conf->mirrors[disk].rdev == NULL || - !conf->mirrors[disk].rdev->in_sync) { + !conf->mirrors[disk].rdev->in_sync || + test_bit(WriteMostly, &conf->mirrors[disk].rdev->flags) + ) { + if (conf->mirrors[disk].rdev && + conf->mirrors[disk].rdev->in_sync) + wonly = disk; if (disk <= 0) disk = conf->raid_disks; disk--; - if (disk == conf->last_used) + if (disk == conf->last_used) { + disk = wonly; break; + } } conf->last_used = disk; atomic_inc(&conf->mirrors[disk].rdev->nr_pending); diff -puN include/linux/raid/md_k.h~md-support-write-mostly-device-in-raid1 include/linux/raid/md_k.h --- 25/include/linux/raid/md_k.h~md-support-write-mostly-device-in-raid1 Wed Aug 17 13:39:23 2005 +++ 25-akpm/include/linux/raid/md_k.h Wed Aug 17 13:39:23 2005 @@ -181,6 +181,9 @@ struct mdk_rdev_s int faulty; /* if faulty do not issue IO requests */ int in_sync; /* device is a full member of the array */ + unsigned long flags; /* Should include faulty and in_sync here. */ +#define WriteMostly 4 /* Avoid reading if at all possible */ + int desc_nr; /* descriptor index in the superblock */ int raid_disk; /* role of device in array */ int saved_raid_disk; /* role that device used to have in the diff -puN include/linux/raid/md_p.h~md-support-write-mostly-device-in-raid1 include/linux/raid/md_p.h --- 25/include/linux/raid/md_p.h~md-support-write-mostly-device-in-raid1 Wed Aug 17 13:39:23 2005 +++ 25-akpm/include/linux/raid/md_p.h Wed Aug 17 13:39:23 2005 @@ -79,6 +79,11 @@ #define MD_DISK_SYNC 2 /* disk is in sync with the raid set */ #define MD_DISK_REMOVED 3 /* disk is in sync with the raid set */ +#define MD_DISK_WRITEMOSTLY 9 /* disk is "write-mostly" is RAID1 config. + * read requests will only be sent here in + * dire need + */ + typedef struct mdp_device_descriptor_s { __u32 number; /* 0 Device number in the entire set */ __u32 major; /* 1 Device major number */ @@ -193,7 +198,7 @@ struct mdp_superblock_1 { __u64 ctime; /* lo 40 bits are seconds, top 24 are microseconds or 0*/ __u32 level; /* -4 (multipath), -1 (linear), 0,1,4,5 */ - __u32 layout; /* only for raid5 currently */ + __u32 layout; /* only for raid5 and raid10 currently */ __u64 size; /* used size of component devices, in 512byte sectors */ __u32 chunksize; /* in 512byte sectors */ @@ -212,7 +217,9 @@ struct mdp_superblock_1 { __u32 dev_number; /* permanent identifier of this device - not role in raid */ __u32 cnt_corrected_read; /* number of read errors that were corrected by re-writing */ __u8 device_uuid[16]; /* user-space setable, ignored by kernel */ - __u8 pad2[64-56]; /* set to 0 when writing */ + __u8 devflags; /* per-device flags. Only one defined...*/ +#define WriteMostly1 1 /* mask for writemostly flag in above */ + __u8 pad2[64-57]; /* set to 0 when writing */ /* array state information - 64 bytes */ __u64 utime; /* 40 bits second, 24 btes microseconds */ _