From: NeilBrown TESTERS WANTED!! SEE BELOW... This patch changes the behaviour of raid5 when it gets a read error. Instead of just failing the device, it tried to find out what should have been there, and writes it over the bad block. For some media-errors, this has a reasonable chance of fixing the error. If the write succeeds, and a subsequent read succeeds as well, raid5 decided the address is OK and conitnues. I have tested this using the 'faulty' md personality, but it would be really good to test it with real disks that have real errors. If anyone has such drives in a cupboard (or even in a computer) and would be willing to give this a try, I would really appreciate it. Instead of failing a drive on read-error, we attempt to re-write the block, and then re-read. If that all works, we allow the device to remain in the array. Signed-off-by: Neil Brown Signed-off-by: Andrew Morton --- drivers/md/raid5.c | 61 +++++++++++++++++++++++++++++++++++++++++---- include/linux/raid/raid5.h | 2 + 2 files changed, 58 insertions(+), 5 deletions(-) diff -puN drivers/md/raid5.c~md-better-handling-of-readerrors-with-raid5 drivers/md/raid5.c --- devel/drivers/md/raid5.c~md-better-handling-of-readerrors-with-raid5 2005-09-15 21:14:43.000000000 -0700 +++ devel-akpm/drivers/md/raid5.c 2005-09-15 21:14:43.000000000 -0700 @@ -349,7 +349,7 @@ static void shrink_stripes(raid5_conf_t conf->slab_cache = NULL; } -static int raid5_end_read_request (struct bio * bi, unsigned int bytes_done, +static int raid5_end_read_request(struct bio * bi, unsigned int bytes_done, int error) { struct stripe_head *sh = bi->bi_private; @@ -401,10 +401,27 @@ static int raid5_end_read_request (struc } #else set_bit(R5_UPTODATE, &sh->dev[i].flags); -#endif +#endif + if (test_bit(R5_ReadError, &sh->dev[i].flags)) { + printk("R5: read error corrected!!\n"); + clear_bit(R5_ReadError, &sh->dev[i].flags); + clear_bit(R5_ReWrite, &sh->dev[i].flags); + } } else { - md_error(conf->mddev, conf->disks[i].rdev); clear_bit(R5_UPTODATE, &sh->dev[i].flags); + if (conf->mddev->degraded) { + printk("R5: read error not correctable.\n"); + clear_bit(R5_ReadError, &sh->dev[i].flags); + clear_bit(R5_ReWrite, &sh->dev[i].flags); + md_error(conf->mddev, conf->disks[i].rdev); + } else if (test_bit(R5_ReWrite, &sh->dev[i].flags)) { + /* Oh, no!!! */ + printk("R5: read error NOT corrected!!\n"); + clear_bit(R5_ReadError, &sh->dev[i].flags); + clear_bit(R5_ReWrite, &sh->dev[i].flags); + md_error(conf->mddev, conf->disks[i].rdev); + } else + set_bit(R5_ReadError, &sh->dev[i].flags); } rdev_dec_pending(conf->disks[i].rdev, conf->mddev); #if 0 @@ -966,6 +983,12 @@ static void handle_stripe(struct stripe_ if (dev->written) written++; rdev = conf->disks[i].rdev; /* FIXME, should I be looking rdev */ if (!rdev || !rdev->in_sync) { + /* The ReadError flag wil just be confusing now */ + clear_bit(R5_ReadError, &dev->flags); + clear_bit(R5_ReWrite, &dev->flags); + } + if (!rdev || !rdev->in_sync + || test_bit(R5_ReadError, &dev->flags)) { failed++; failed_num = i; } else @@ -980,6 +1003,14 @@ static void handle_stripe(struct stripe_ if (failed > 1 && to_read+to_write+written) { for (i=disks; i--; ) { int bitmap_end = 0; + + if (test_bit(R5_ReadError, &sh->dev[i].flags)) { + mdk_rdev_t *rdev = conf->disks[i].rdev; + if (rdev && rdev->in_sync) + /* multiple read failures in one stripe */ + md_error(conf->mddev, rdev); + } + spin_lock_irq(&conf->device_lock); /* fail all writes first */ bi = sh->dev[i].towrite; @@ -1015,7 +1046,8 @@ static void handle_stripe(struct stripe_ } /* fail any reads if this device is non-operational */ - if (!test_bit(R5_Insync, &sh->dev[i].flags)) { + if (!test_bit(R5_Insync, &sh->dev[i].flags) || + test_bit(R5_ReadError, &sh->dev[i].flags)) { bi = sh->dev[i].toread; sh->dev[i].toread = NULL; if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags)) @@ -1274,7 +1306,26 @@ static void handle_stripe(struct stripe_ md_done_sync(conf->mddev, STRIPE_SECTORS,1); clear_bit(STRIPE_SYNCING, &sh->state); } - + + /* If the failed drive is just a ReadError, then we might need to progress + * the repair/check process + */ + if (failed == 1 && test_bit(R5_ReadError, &sh->dev[failed_num].flags) + && !test_bit(R5_LOCKED, &sh->dev[failed_num].flags) + && test_bit(R5_UPTODATE, &sh->dev[failed_num].flags) + ) { + dev = &sh->dev[failed_num]; + if (!test_bit(R5_ReWrite, &dev->flags)) { + set_bit(R5_Wantwrite, &dev->flags); + set_bit(R5_ReWrite, &dev->flags); + set_bit(R5_LOCKED, &dev->flags); + } else { + /* let's read it back */ + set_bit(R5_Wantread, &dev->flags); + set_bit(R5_LOCKED, &dev->flags); + } + } + spin_unlock(&sh->lock); while ((bi=return_bi)) { diff -puN include/linux/raid/raid5.h~md-better-handling-of-readerrors-with-raid5 include/linux/raid/raid5.h --- devel/include/linux/raid/raid5.h~md-better-handling-of-readerrors-with-raid5 2005-09-15 21:14:43.000000000 -0700 +++ devel-akpm/include/linux/raid/raid5.h 2005-09-15 21:14:43.000000000 -0700 @@ -154,6 +154,8 @@ struct stripe_head { #define R5_Wantwrite 5 #define R5_Syncio 6 /* this io need to be accounted as resync io */ #define R5_Overlap 7 /* There is a pending overlapping request on this block */ +#define R5_ReadError 8 /* seen a read error here recently */ +#define R5_ReWrite 9 /* have tried to over-write the readerror */ /* * Write method _