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/web/templates/zfs.html

@@ -13,6 +13,7 @@
     <div><span class="muted">fragmentation</span> {{.FragPct}}%</div>
     <div><span class="muted">last scrub</span> {{if .LastScrub}}{{dtp .LastScrub}} ({{agop .LastScrub}}){{else}}never{{end}}</div>
     <div><span class="muted">errors</span> {{if .Errors}}{{.Errors}}{{else}}—{{end}}</div>
+    <div><span class="muted">dedup</span> {{with index $.Data.PoolDedup .Name}}{{.}}{{else}}—{{end}}{{if .DedupRatio}} (ratio {{printf "%.2f" .DedupRatio}}x){{end}}</div>
   </div>
   <div class="bar"><span class="fill {{capClass .CapPct $.Data.Th.PoolCapacityPct 95}}" style="width:{{.CapPct}}%"></span></div>
   {{if .Scan}}<p class="small"><span class="muted">scan:</span> {{.Scan}}</p>{{end}}
@@ -31,6 +32,21 @@
     {{end}}
     </tbody>
   </table></div>
+  {{$dedup := index $.Data.PoolDedup .Name}}
+  <details class="dedup dedup-{{.Name}}">
+    <summary>Deduplication</summary>
+    <form method="post" action="/zfs/dedup" class="inline">
+      <input type="hidden" name="pool" value="{{.Name}}">
+      <label>Dedup for {{.Name}}
+        <select name="dedup">
+          <option value="off" {{if or (eq $dedup "off") (eq $dedup "")}}selected{{end}}>off</option>
+          <option value="on" {{if and (ne $dedup "off") (ne $dedup "")}}selected{{end}}>on</option>
+        </select>
+      </label>
+      <button type="submit">Apply</button>
+    </form>
+    <p class="small muted">Sets dedup on the pool root dataset; child datasets inherit it unless they override it. Only newly written data is deduplicated, and turning it off keeps the existing dedup table. The dedup table needs a lot of RAM (up to ~5 GB per 1 TB of unique data) &mdash; enable it only for data with many duplicate blocks.</p>
+  </details>
   <details class="newds newds-{{.Name}}" {{if eq $form.Pool .Name}}open{{end}}>
     <summary>New dataset in {{.Name}}</summary>
     <form method="post" action="/zfs/create" class="ds-form">
@@ -46,6 +62,13 @@
             <option value="off" {{if eq $form.Compression "off"}}selected{{end}}>off</option>
           </select>
         </label>
+        <label>Dedup
+          <select name="dedup">
+            <option value="" {{if eq $form.Dedup ""}}selected{{end}}>inherit</option>
+            <option value="on" {{if eq $form.Dedup "on"}}selected{{end}}>on</option>
+            <option value="off" {{if eq $form.Dedup "off"}}selected{{end}}>off</option>
+          </select>
+        </label>
         <label>Quota <input name="quota" placeholder="none, or 100G / 1.5T" value="{{if eq $form.Pool .Name}}{{$form.Quota}}{{end}}"></label>
       </div>
       <p class="small muted">Creates {{.Name}}/&lt;name&gt; (parents are created too), mounts it at /{{.Name}}/&lt;name&gt; and chowns the mountpoint to the owner.</p>