diff options
Diffstat (limited to 'sys/contrib/openzfs/module/zfs/vdev_removal.c')
| -rw-r--r-- | sys/contrib/openzfs/module/zfs/vdev_removal.c | 80 |
1 files changed, 58 insertions, 22 deletions
diff --git a/sys/contrib/openzfs/module/zfs/vdev_removal.c b/sys/contrib/openzfs/module/zfs/vdev_removal.c index 2f7a739da241..abb71543e3ab 100644 --- a/sys/contrib/openzfs/module/zfs/vdev_removal.c +++ b/sys/contrib/openzfs/module/zfs/vdev_removal.c @@ -51,34 +51,70 @@ #include <sys/trace_zfs.h> /* - * This file contains the necessary logic to remove vdevs from a - * storage pool. Currently, the only devices that can be removed - * are log, cache, and spare devices; and top level vdevs from a pool - * w/o raidz or mirrors. (Note that members of a mirror can be removed - * by the detach operation.) + * This file contains the necessary logic to remove vdevs from a storage + * pool. Note that members of a mirror can be removed by the detach + * operation. Currently, the only devices that can be removed are: * - * Log vdevs are removed by evacuating them and then turning the vdev - * into a hole vdev while holding spa config locks. + * 1) Traditional hot spare and cache vdevs. Note that draid distributed + * spares are fixed at creation time and cannot be removed. * - * Top level vdevs are removed and converted into an indirect vdev via - * a multi-step process: + * 2) Log vdevs are removed by evacuating them and then turning the vdev + * into a hole vdev while holding spa config locks. * - * - Disable allocations from this device (spa_vdev_remove_top). + * 3) Top-level singleton and mirror vdevs, including dedup and special + * vdevs, are removed and converted into an indirect vdev via a + * multi-step process: * - * - From a new thread (spa_vdev_remove_thread), copy data from - * the removing vdev to a different vdev. The copy happens in open - * context (spa_vdev_copy_impl) and issues a sync task - * (vdev_mapping_sync) so the sync thread can update the partial - * indirect mappings in core and on disk. + * - Disable allocations from this device (spa_vdev_remove_top). * - * - If a free happens during a removal, it is freed from the - * removing vdev, and if it has already been copied, from the new - * location as well (free_from_removing_vdev). + * - From a new thread (spa_vdev_remove_thread), copy data from the + * removing vdev to a different vdev. The copy happens in open context + * (spa_vdev_copy_impl) and issues a sync task (vdev_mapping_sync) so + * the sync thread can update the partial indirect mappings in core + * and on disk. * - * - After the removal is completed, the copy thread converts the vdev - * into an indirect vdev (vdev_remove_complete) before instructing - * the sync thread to destroy the space maps and finish the removal - * (spa_finish_removal). + * - If a free happens during a removal, it is freed from the removing + * vdev, and if it has already been copied, from the new location as + * well (free_from_removing_vdev). + * + * - After the removal is completed, the copy thread converts the vdev + * into an indirect vdev (vdev_remove_complete) before instructing + * the sync thread to destroy the space maps and finish the removal + * (spa_finish_removal). + * + * The following constraints currently apply primary device removal: + * + * - All vdevs must be online, healthy, and not be missing any data + * according to the DTLs. + * + * - When removing a singleton or mirror vdev, regardless of it's a + * special, dedup, or primary device, it must have the same ashift + * as the devices in the normal allocation class. Furthermore, all + * vdevs in the normal allocation class must have the same ashift to + * ensure the new allocations never includes additional padding. + * + * - The normal allocation class cannot contain any raidz or draid + * top-level vdevs since segments are copied without regard for block + * boundaries. This makes it impossible to calculate the required + * parity columns when using these vdev types as the destination. + * + * - The encryption keys must be loaded so the ZIL logs can be reset + * in order to prevent writing to the device being removed. + * + * N.B. ashift and raidz/draid constraints for primary top-level device + * removal could be slightly relaxed if it were possible to request that + * DVAs from a mirror or singleton in the specified allocation class be + * used (metaslab_alloc_dva). + * + * This flexibility would be particularly useful for raidz/draid pools which + * often include a mirrored special device. If a mistakenly added top-level + * singleton were added it could then still be removed at the cost of some + * special device capacity. This may be a worthwhile tradeoff depending on + * the pool capacity and expense (cost, complexity, time) of creating a new + * pool and copying all of the data to correct the configuration. + * + * Furthermore, while not currently supported it should be possible to allow + * vdevs of any type to be removed as long as they've never been written to. */ typedef struct vdev_copy_arg { |