diff options
Diffstat (limited to 'module/zfs/vdev_raidz.c')
| -rw-r--r-- | module/zfs/vdev_raidz.c | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/module/zfs/vdev_raidz.c b/module/zfs/vdev_raidz.c index 130ec575e..d2dfd5b43 100644 --- a/module/zfs/vdev_raidz.c +++ b/module/zfs/vdev_raidz.c @@ -431,23 +431,50 @@ static const zio_vsd_ops_t vdev_raidz_vsd_ops = { vdev_raidz_cksum_report }; +/* + * Divides the IO evenly across all child vdevs; usually, dcols is + * the number of children in the target vdev. + */ static raidz_map_t * vdev_raidz_map_alloc(zio_t *zio, uint64_t unit_shift, uint64_t dcols, uint64_t nparity) { raidz_map_t *rm; + /* The starting RAIDZ (parent) vdev sector of the block. */ uint64_t b = zio->io_offset >> unit_shift; + /* The zio's size in units of the vdev's minimum sector size. */ uint64_t s = zio->io_size >> unit_shift; + /* The first column for this stripe. */ uint64_t f = b % dcols; + /* The starting byte offset on each child vdev. */ uint64_t o = (b / dcols) << unit_shift; uint64_t q, r, c, bc, col, acols, scols, coff, devidx, asize, tot; + /* + * "Quotient": The number of data sectors for this stripe on all but + * the "big column" child vdevs that also contain "remainder" data. + */ q = s / (dcols - nparity); + + /* + * "Remainder": The number of partial stripe data sectors in this I/O. + * This will add a sector to some, but not all, child vdevs. + */ r = s - q * (dcols - nparity); + + /* The number of "big columns" - those which contain remainder data. */ bc = (r == 0 ? 0 : r + nparity); + + /* + * The total number of data and parity sectors associated with + * this I/O. + */ tot = s + nparity * (q + (r == 0 ? 0 : 1)); + /* acols: The columns that will be accessed. */ + /* scols: The columns that will be accessed or skipped. */ if (q == 0) { + /* Our I/O request doesn't span all child vdevs. */ acols = bc; scols = MIN(dcols, roundup(bc, nparity + 1)); } else { @@ -1521,6 +1548,23 @@ vdev_raidz_child_done(zio_t *zio) rc->rc_skipped = 0; } +/* + * Start an IO operation on a RAIDZ VDev + * + * Outline: + * - For write operations: + * 1. Generate the parity data + * 2. Create child zio write operations to each column's vdev, for both + * data and parity. + * 3. If the column skips any sectors for padding, create optional dummy + * write zio children for those areas to improve aggregation continuity. + * - For read operations: + * 1. Create child zio read operations to each data column's vdev to read + * the range of data required for zio. + * 2. If this is a scrub or resilver operation, or if any of the data + * vdevs have had errors, then create zio read operations to the parity + * columns' VDevs as well. + */ static int vdev_raidz_io_start(zio_t *zio) { @@ -1864,6 +1908,27 @@ done: return (ret); } +/* + * Complete an IO operation on a RAIDZ VDev + * + * Outline: + * - For write operations: + * 1. Check for errors on the child IOs. + * 2. Return, setting an error code if too few child VDevs were written + * to reconstruct the data later. Note that partial writes are + * considered successful if they can be reconstructed at all. + * - For read operations: + * 1. Check for errors on the child IOs. + * 2. If data errors occurred: + * a. Try to reassemble the data from the parity available. + * b. If we haven't yet read the parity drives, read them now. + * c. If all parity drives have been read but the data still doesn't + * reassemble with a correct checksum, then try combinatorial + * reconstruction. + * d. If that doesn't work, return an error. + * 3. If there were unexpected errors or this is a resilver operation, + * rewrite the vdevs that had errors. + */ static void vdev_raidz_io_done(zio_t *zio) { |