ZFS: dedup toggle per pool and dedup option for new datasets

Pool cards show the dedup ratio and can set dedup=on|off on the pool root
dataset (inherited by children); the new-dataset form gets a dedup option.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/zfsadm/zfsadm.go

@@ -1,5 +1,5 @@
 // Package zfsadm performs the few mutating ZFS operations the UI offers
-// (create / destroy datasets). Commands go through a Runner so they can be
+// (create / destroy datasets, toggle pool dedup). Commands go through a Runner so they can be
 // executed on the host via systemd-run: nasmon runs in a sandboxed mount
 // namespace (ProtectSystem=strict), where a plain "zfs create" would mount the
 // new dataset only inside the service and leave the host without it.
@@ -59,6 +59,7 @@ func (a *Admin) ctx() (context.Context, context.CancelFunc) {
 // CreateOpts are the user-visible knobs of "zfs create".
 type CreateOpts struct {
 	Compression string // "", lz4, zstd, off ("" = inherit)
+	Dedup       string // "", on, off ("" = inherit)
 	Quota       string // "", or a size like 100G / 1.5T
 	Owner       string // uid:gid applied to the mountpoint; "" = leave root
 }
@@ -71,6 +72,9 @@ func (a *Admin) Create(full string, o CreateOpts) error {
 	if err := ValidateCompression(o.Compression); err != nil {
 		return err
 	}
+	if err := ValidateDedup(o.Dedup); err != nil {
+		return err
+	}
 	if err := ValidateSize(o.Quota); err != nil {
 		return err
 	}
@@ -81,6 +85,9 @@ func (a *Admin) Create(full string, o CreateOpts) error {
 	if o.Compression != "" {
 		args = append(args, "-o", "compression="+o.Compression)
 	}
+	if o.Dedup != "" {
+		args = append(args, "-o", "dedup="+o.Dedup)
+	}
 	if o.Quota != "" {
 		args = append(args, "-o", "quota="+o.Quota)
 	}
@@ -106,6 +113,25 @@ func (a *Admin) Create(full string, o CreateOpts) error {
 	return nil
 }
 
+// SetDedup sets the dedup property (on/off) on the root dataset of pool, so it
+// applies to every dataset that does not override it. Only newly written
+// blocks are affected either way.
+func (a *Admin) SetDedup(pool, value string) error {
+	if err := ValidateFullName(pool); err != nil {
+		return err
+	}
+	if strings.Contains(pool, "/") {
+		return errors.New("dedup is set on the pool root dataset only")
+	}
+	if value != "on" && value != "off" {
+		return errors.New("dedup must be on or off")
+	}
+	ctx, cancel := a.ctx()
+	defer cancel()
+	_, err := a.Run(ctx, "zfs", "set", "dedup="+value, pool)
+	return err
+}
+
 // EmptyRefer is the upper bound of "referenced" bytes for a dataset we still
 // consider empty (a fresh dataset refers ~96-128 KiB of metadata).
 const EmptyRefer = 1 << 20
@@ -206,6 +232,14 @@ func ValidateCompression(s string) error {
 	return errors.New("compression must be inherit, lz4, zstd or off")
 }
 
+func ValidateDedup(s string) error {
+	switch s {
+	case "", "on", "off":
+		return nil
+	}
+	return errors.New("dedup must be inherit, on or off")
+}
+
 func ValidateOwner(s string) error {
 	if s == "" || reOwner.MatchString(s) {
 		return nil