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Remove dedupditto functionality

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If dedup is in use, the `dedupditto` property can be set, causing ZFS to
keep an extra copy of data that is referenced many times (>100x).  The
idea was that this data is more important than other data and thus we
want to be really sure that it is not lost if the disk experiences a
small amount of random corruption.

ZFS (and system administrators) rely on the pool-level redundancy to
protect their data (e.g. mirroring or RAIDZ).  Since the user/sysadmin
doesn't have control over what data will be offered extra redundancy by
dedupditto, this extra redundancy is not very useful.  The bulk of the
data is still vulnerable to loss based on the pool-level redundancy.
For example, if particle strikes corrupt 0.1% of blocks, you will either
be saved by mirror/raidz, or you will be sad.  This is true even if
dedupditto saved another 0.01% of blocks from being corrupted.

Therefore, the dedupditto functionality is rarely enabled (i.e. the
property is rarely set), and it fulfills its promise of increased
redundancy even more rarely.

Additionally, this feature does not work as advertised (on existing
releases), because scrub/resilver did not repair the extra (dedupditto)
copy (see https://github.com/zfsonlinux/zfs/pull/8270).

In summary, this seldom-used feature doesn't work, and even if it did it
wouldn't provide useful data protection.  It has a non-trivial
maintenance burden (again see https://github.com/zfsonlinux/zfs/pull/8270).

We should remove the dedupditto functionality.  For backwards
compatibility with the existing CLI, "zpool set dedupditto" will still
"succeed" (exit code zero), but won't have any effect.  For backwards
compatibility with existing pools that had dedupditto enabled at some
point, the code will still be able to understand dedupditto blocks and
free them when appropriate.  However, ZFS won't write any new dedupditto
blocks.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Alek Pinchuk <apinchuk@datto.com>
Issue #8270 
Closes #8310
This commit is contained in:
Matthew Ahrens
2019-06-19 14:54:02 -07:00
committed by Brian Behlendorf
parent fb0be12d7b
commit 050d720c43
12 changed files with 22 additions and 340 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/ddt.c
+8 -64
View File
@@ -552,65 +552,6 @@ ddt_get_pool_dedup_ratio(spa_t *spa)
return (dds_total.dds_ref_dsize * 100 / dds_total.dds_dsize);
}
int
ddt_ditto_copies_needed(ddt_t *ddt, ddt_entry_t *dde, ddt_phys_t *ddp_willref)
{
spa_t *spa = ddt->ddt_spa;
uint64_t total_refcnt = 0;
uint64_t ditto = spa->spa_dedup_ditto;
int total_copies = 0;
int desired_copies = 0;
int copies_needed = 0;
for (int p = DDT_PHYS_SINGLE; p <= DDT_PHYS_TRIPLE; p++) {
ddt_phys_t *ddp = &dde->dde_phys[p];
zio_t *zio = dde->dde_lead_zio[p];
uint64_t refcnt = ddp->ddp_refcnt; /* committed refs */
if (zio != NULL)
refcnt += zio->io_parent_count; /* pending refs */
if (ddp == ddp_willref)
refcnt++; /* caller's ref */
if (refcnt != 0) {
total_refcnt += refcnt;
total_copies += p;
}
}
if (ditto == 0 || ditto > UINT32_MAX)
ditto = UINT32_MAX;
if (total_refcnt >= 1)
desired_copies++;
if (total_refcnt >= ditto)
desired_copies++;
if (total_refcnt >= ditto * ditto)
desired_copies++;
copies_needed = MAX(desired_copies, total_copies) - total_copies;
/* encrypted blocks store their IV in DVA[2] */
if (DDK_GET_CRYPT(&dde->dde_key))
copies_needed = MIN(copies_needed, SPA_DVAS_PER_BP - 1);
return (copies_needed);
}
int
ddt_ditto_copies_present(ddt_entry_t *dde)
{
ddt_phys_t *ddp = &dde->dde_phys[DDT_PHYS_DITTO];
dva_t *dva = ddp->ddp_dva;
int copies = 0 - DVA_GET_GANG(dva);
for (int d = 0; d < DDE_GET_NDVAS(dde); d++, dva++)
if (DVA_IS_VALID(dva))
copies++;
ASSERT(copies >= 0 && copies < SPA_DVAS_PER_BP);
return (copies);
}
size_t
ddt_compress(void *src, uchar_t *dst, size_t s_len, size_t d_len)
{
@@ -1088,8 +1029,11 @@ ddt_sync_entry(ddt_t *ddt, ddt_entry_t *dde, dmu_tx_t *tx, uint64_t txg)
continue;
}
if (p == DDT_PHYS_DITTO) {
if (ddt_ditto_copies_needed(ddt, dde, NULL) == 0)
ddt_phys_free(ddt, ddk, ddp, txg);
/*
* Note, we no longer create DDT-DITTO blocks, but we
* don't want to leak any written by older software.
*/
ddt_phys_free(ddt, ddk, ddp, txg);
continue;
}
if (ddp->ddp_refcnt == 0)
@@ -1097,9 +1041,9 @@ ddt_sync_entry(ddt_t *ddt, ddt_entry_t *dde, dmu_tx_t *tx, uint64_t txg)
total_refcnt += ddp->ddp_refcnt;
}
if (dde->dde_phys[DDT_PHYS_DITTO].ddp_phys_birth != 0)
nclass = DDT_CLASS_DITTO;
else if (total_refcnt > 1)
/* We do not create new DDT-DITTO blocks. */
ASSERT0(dde->dde_phys[DDT_PHYS_DITTO].ddp_phys_birth);
if (total_refcnt > 1)
nclass = DDT_CLASS_DUPLICATE;
else
nclass = DDT_CLASS_UNIQUE;
module/zfs/spa.c
+3 -15
View File
@@ -694,16 +694,6 @@ spa_prop_validate(spa_t *spa, nvlist_t *props)
error = SET_ERROR(E2BIG);
break;
case ZPOOL_PROP_DEDUPDITTO:
if (spa_version(spa) < SPA_VERSION_DEDUP)
error = SET_ERROR(ENOTSUP);
else
error = nvpair_value_uint64(elem, &intval);
if (error == 0 &&
intval != 0 && intval < ZIO_DEDUPDITTO_MIN)
error = SET_ERROR(EINVAL);
break;
default:
break;
}
@@ -712,6 +702,9 @@ spa_prop_validate(spa_t *spa, nvlist_t *props)
break;
}
(void) nvlist_remove_all(props,
zpool_prop_to_name(ZPOOL_PROP_DEDUPDITTO));
if (!error && reset_bootfs) {
error = nvlist_remove(props,
zpool_prop_to_name(ZPOOL_PROP_BOOTFS), DATA_TYPE_STRING);
@@ -3604,8 +3597,6 @@ spa_ld_get_props(spa_t *spa)
spa_prop_find(spa, ZPOOL_PROP_FAILUREMODE, &spa->spa_failmode);
spa_prop_find(spa, ZPOOL_PROP_AUTOEXPAND, &spa->spa_autoexpand);
spa_prop_find(spa, ZPOOL_PROP_MULTIHOST, &spa->spa_multihost);
spa_prop_find(spa, ZPOOL_PROP_DEDUPDITTO,
&spa->spa_dedup_ditto);
spa_prop_find(spa, ZPOOL_PROP_AUTOTRIM, &spa->spa_autotrim);
spa->spa_autoreplace = (autoreplace != 0);
}
@@ -7983,9 +7974,6 @@ spa_sync_props(void *arg, dmu_tx_t *tx)
case ZPOOL_PROP_MULTIHOST:
spa->spa_multihost = intval;
break;
case ZPOOL_PROP_DEDUPDITTO:
spa->spa_dedup_ditto = intval;
break;
default:
break;
}
module/zfs/zio.c
-68
View File
@@ -3118,35 +3118,6 @@ zio_ddt_child_write_done(zio_t *zio)
ddt_exit(ddt);
}
static void
zio_ddt_ditto_write_done(zio_t *zio)
{
int p = DDT_PHYS_DITTO;
ASSERTV(zio_prop_t *zp = &zio->io_prop);
blkptr_t *bp = zio->io_bp;
ddt_t *ddt = ddt_select(zio->io_spa, bp);
ddt_entry_t *dde = zio->io_private;
ddt_phys_t *ddp = &dde->dde_phys[p];
ddt_key_t *ddk = &dde->dde_key;
ddt_enter(ddt);
ASSERT(ddp->ddp_refcnt == 0);
ASSERT(dde->dde_lead_zio[p] == zio);
dde->dde_lead_zio[p] = NULL;
if (zio->io_error == 0) {
ASSERT(ZIO_CHECKSUM_EQUAL(bp->blk_cksum, ddk->ddk_cksum));
ASSERT(zp->zp_copies < SPA_DVAS_PER_BP);
ASSERT(zp->zp_copies == BP_GET_NDVAS(bp) - BP_IS_GANG(bp));
if (ddp->ddp_phys_birth != 0)
ddt_phys_free(ddt, ddk, ddp, zio->io_txg);
ddt_phys_fill(ddp, bp);
}
ddt_exit(ddt);
}
static zio_t *
zio_ddt_write(zio_t *zio)
{
@@ -3155,9 +3126,7 @@ zio_ddt_write(zio_t *zio)
uint64_t txg = zio->io_txg;
zio_prop_t *zp = &zio->io_prop;
int p = zp->zp_copies;
int ditto_copies;
zio_t *cio = NULL;
zio_t *dio = NULL;
ddt_t *ddt = ddt_select(spa, bp);
ddt_entry_t *dde;
ddt_phys_t *ddp;
@@ -3192,41 +3161,6 @@ zio_ddt_write(zio_t *zio)
return (zio);
}
ditto_copies = ddt_ditto_copies_needed(ddt, dde, ddp);
ASSERT(ditto_copies < SPA_DVAS_PER_BP);
if (ditto_copies > ddt_ditto_copies_present(dde) &&
dde->dde_lead_zio[DDT_PHYS_DITTO] == NULL) {
zio_prop_t czp = *zp;
czp.zp_copies = ditto_copies;
/*
* If we arrived here with an override bp, we won't have run
* the transform stack, so we won't have the data we need to
* generate a child i/o. So, toss the override bp and restart.
* This is safe, because using the override bp is just an
* optimization; and it's rare, so the cost doesn't matter.
*/
if (zio->io_bp_override) {
zio_pop_transforms(zio);
zio->io_stage = ZIO_STAGE_OPEN;
zio->io_pipeline = ZIO_WRITE_PIPELINE;
zio->io_bp_override = NULL;
BP_ZERO(bp);
ddt_exit(ddt);
return (zio);
}
dio = zio_write(zio, spa, txg, bp, zio->io_orig_abd,
zio->io_orig_size, zio->io_orig_size, &czp, NULL, NULL,
NULL, zio_ddt_ditto_write_done, dde, zio->io_priority,
ZIO_DDT_CHILD_FLAGS(zio), &zio->io_bookmark);
zio_push_transform(dio, zio->io_abd, zio->io_size, 0, NULL);
dde->dde_lead_zio[DDT_PHYS_DITTO] = dio;
}
if (ddp->ddp_phys_birth != 0 || dde->dde_lead_zio[p] != NULL) {
if (ddp->ddp_phys_birth != 0)
ddt_bp_fill(ddp, bp, txg);
@@ -3254,8 +3188,6 @@ zio_ddt_write(zio_t *zio)
if (cio)
zio_nowait(cio);
if (dio)
zio_nowait(dio);
return (zio);
}