diff --git a/README.md b/README.md
index 8398efd..8d0bc89 100644
--- a/README.md
+++ b/README.md
@@ -45,7 +45,7 @@ https://yourcmc.ru/git/vitalif/vitastor/
   AFR сервера эмпирически поделен на число дисков, чтобы "размазать" вероятность отказа сервера
   по его дискам.
 
-Парадоксы дней рождений:
+## Парадокс дней рождений
 
 - PG почти гарантированно пересекаются, особенно в небольших кластерах. Степень их пересечения
   очень полезно учитывать.
diff --git a/afr.js b/afr.js
index b0fde1d..d3dcfb1 100644
--- a/afr.js
+++ b/afr.js
@@ -55,7 +55,8 @@ function failure_rate_fullmesh(n, a, f)
 // is that, with k=2, total failure rate doesn't depend on number of peers per OSD,
 // because it gets increased linearly by increased number of peers to fail
 // and decreased linearly by reduced rebalance time.
-function cluster_afr({ n_hosts, n_drives, afr_drive, afr_host, capacity, speed, ec, ec_data, ec_parity, replicas, pgs = 1, osd_rm, degraded_replacement, down_out_interval = 600 })
+function cluster_afr({ n_hosts, n_drives, afr_drive, afr_host, capacity, speed, disk_heal_hours, host_heal_hours,
+    ec, ec_data, ec_parity, replicas, pgs = 1, osd_rm, degraded_replacement, down_out_interval = 0 })
 {
     const pg_size = (ec ? ec_data+ec_parity : replicas);
     // <peers> is a number of non-intersecting PGs that a single OSD/drive has on average
@@ -66,8 +67,18 @@ function cluster_afr({ n_hosts, n_drives, afr_drive, afr_host, capacity, speed,
     const resilver_peers = n_drives == 1 || osd_rm ? avg_distinct((n_hosts-1)*n_drives, pgs) : avg_distinct(n_drives-1, pgs);
     // <host_resilver_peers> other drives participate in resilvering of a failed host
     const host_resilver_peers = avg_distinct((n_hosts-1)*n_drives, n_drives*pgs);
-    const disk_heal_time = (down_out_interval + capacity/(degraded_replacement ? 1 : resilver_peers)/speed)/86400/365;
-    const host_heal_time = (down_out_interval + n_drives*capacity/host_resilver_peers/speed)/86400/365;
+    let disk_heal_time, host_heal_time;
+    if (speed)
+        disk_heal_time = (down_out_interval + capacity/(degraded_replacement ? 1 : resilver_peers)/speed)/86400/365;
+    else
+    {
+        disk_heal_time = disk_heal_hours/24/365;
+        speed = capacity / (degraded_replacement ? 1 : resilver_peers) / (disk_heal_hours*3600 - down_out_interval);
+    }
+    if (host_heal_hours)
+        host_heal_time = host_heal_hours/24/365;
+    else
+        host_heal_time = (down_out_interval + n_drives*capacity/host_resilver_peers/speed)/86400/365;
     const disk_heal_fail = ((afr_drive+afr_host/n_drives)*disk_heal_time);
     const host_heal_fail = ((afr_drive+afr_host/n_drives)*host_heal_time);
     const disk_pg_fail = ec
diff --git a/fontello/config.json b/fontello/config.json
new file mode 100644
index 0000000..17b57bf
--- /dev/null
+++ b/fontello/config.json
@@ -0,0 +1,24 @@
+{
+  "name": "fontello",
+  "css_prefix_text": "icon-",
+  "css_use_suffix": false,
+  "hinting": true,
+  "units_per_em": 1000,
+  "ascent": 850,
+  "glyphs": [
+    {
+      "uid": "0430f56230dd33f67f26be82b07a84fc",
+      "css": "arw-down",
+      "code": 59412,
+      "src": "custom_icons",
+      "selected": true,
+      "svg": {
+        "path": "M800 956C828.7 956 857.4 945.1 879.2 923.2L1567.2 235.2C1610.9 191.5 1610.9 120.5 1567.2 76.8 1523.4 33 1452.5 33 1408.7 76.8L800 685.5 191.3 76.8C147.5 33.1 76.6 33.1 32.8 76.8-10.9 120.6-10.9 191.5 32.8 235.3L720.8 923.2C742.7 945.1 771.3 956 800 956Z",
+        "width": 1600
+      },
+      "search": [
+        "arw-down"
+      ]
+    }
+  ]
+}
\ No newline at end of file
diff --git a/fontello/css/fontello.css b/fontello/css/fontello.css
new file mode 100644
index 0000000..864b169
--- /dev/null
+++ b/fontello/css/fontello.css
@@ -0,0 +1,57 @@
+@font-face {
+  font-family: 'fontello';
+  src: url('../font/fontello.eot?162972');
+  src: url('../font/fontello.eot?162972#iefix') format('embedded-opentype'),
+       url('../font/fontello.woff2?162972') format('woff2'),
+       url('../font/fontello.woff?162972') format('woff'),
+       url('../font/fontello.ttf?162972') format('truetype'),
+       url('../font/fontello.svg?162972#fontello') format('svg');
+  font-weight: normal;
+  font-style: normal;
+}
+/* Chrome hack: SVG is rendered more smooth in Windozze. 100% magic, uncomment if you need it. */
+/* Note, that will break hinting! In other OS-es font will be not as sharp as it could be */
+/*
+@media screen and (-webkit-min-device-pixel-ratio:0) {
+  @font-face {
+    font-family: 'fontello';
+    src: url('../font/fontello.svg?162972#fontello') format('svg');
+  }
+}
+*/
+[class^="icon-"]:before, [class*=" icon-"]:before {
+  font-family: "fontello";
+  font-style: normal;
+  font-weight: normal;
+  speak: never;
+
+  display: inline-block;
+  text-decoration: inherit;
+  width: 1em;
+  margin-right: .2em;
+  text-align: center;
+  /* opacity: .8; */
+
+  /* For safety - reset parent styles, that can break glyph codes*/
+  font-variant: normal;
+  text-transform: none;
+
+  /* fix buttons height, for twitter bootstrap */
+  line-height: 1em;
+
+  /* Animation center compensation - margins should be symmetric */
+  /* remove if not needed */
+  margin-left: .2em;
+
+  /* you can be more comfortable with increased icons size */
+  /* font-size: 120%; */
+
+  /* Font smoothing. That was taken from TWBS */
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+
+  /* Uncomment for 3D effect */
+  /* text-shadow: 1px 1px 1px rgba(127, 127, 127, 0.3); */
+}
+
+.icon-arw-down:before { content: '\e814'; } /* '' */
diff --git a/fontello/font/fontello.eot b/fontello/font/fontello.eot
new file mode 100644
index 0000000..acea786
Binary files /dev/null and b/fontello/font/fontello.eot differ
diff --git a/fontello/font/fontello.svg b/fontello/font/fontello.svg
new file mode 100644
index 0000000..2c8ae03
--- /dev/null
+++ b/fontello/font/fontello.svg
@@ -0,0 +1,12 @@
+<?xml version="1.0" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<svg xmlns="http://www.w3.org/2000/svg">
+<metadata>Copyright (C) 2021 by original authors @ fontello.com</metadata>
+<defs>
+<font id="fontello" horiz-adv-x="1000" >
+<font-face font-family="fontello" font-weight="400" font-stretch="normal" units-per-em="1000" ascent="850" descent="-150" />
+<missing-glyph horiz-adv-x="1000" />
+<glyph glyph-name="arw-down" unicode="&#xe814;" d="M800-106c29 0 57 11 79 33l688 688c44 44 44 115 0 158-44 44-114 44-158 0l-609-608-609 608c-43 44-114 44-158 0-44-44-44-114 0-158l688-688c22-22 50-33 79-33z" horiz-adv-x="1600" />
+</font>
+</defs>
+</svg>
diff --git a/fontello/font/fontello.ttf b/fontello/font/fontello.ttf
new file mode 100644
index 0000000..68135f4
Binary files /dev/null and b/fontello/font/fontello.ttf differ
diff --git a/fontello/font/fontello.woff b/fontello/font/fontello.woff
new file mode 100644
index 0000000..7e14b57
Binary files /dev/null and b/fontello/font/fontello.woff differ
diff --git a/fontello/font/fontello.woff2 b/fontello/font/fontello.woff2
new file mode 100644
index 0000000..2d7d22f
Binary files /dev/null and b/fontello/font/fontello.woff2 differ
diff --git a/index.html b/index.html
index 4170695..5a5a4e2 100644
--- a/index.html
+++ b/index.html
@@ -4,6 +4,7 @@
 <title>Калькулятор вероятности отказа кластера Ceph/Vitastor</title>
 <meta name="viewport" content="width=790px, initial-scale=1">
 <meta charset="utf-8" />
+<link rel="stylesheet" href="fontello/css/fontello.css" />
 <style>
 * { box-sizing: border-box; }
 body { margin: 0; font-size: 15px; font-family: Arial, Helvetica, sans-serif; }
@@ -18,6 +19,14 @@ input[type="text"] { border: 1px solid #aaa; padding: 4px; border-radius: 3px; }
 .switch.r { border-left-width: 0; border-radius: 0 20px 20px 0; padding-right: 15px; }
 .switch.sel { border-color: #08f; background: #08f; color: white; }
 .switch:hover { border-color: #4af; background: #4af; color: white; }
+.icombo { display: inline-block; position: relative; border: 1px solid #aaa; border-radius: 3px; padding: 2px 8px 2px 5px; cursor: pointer; transition: 0.2s ease-out; }
+.icombo .icon-arw-down { font-size: 7px; display: inline-block; vertical-align: middle; color: #aaa; transition: 0.2s ease-out; }
+.icombo:hover { border-color: #4af; background: #4af; color: white; }
+.icombo:hover .icon-arw-down { color: white; }
+.icombo .options { opacity: 0; position: absolute; top: 100%; left: -1px; width: 150px; background: white; color: black; border-radius: 3px; overflow: hidden; cursor: pointer; transition: 0.2s ease-out; box-shadow: 0 0 10px 3px rgba(0, 0, 0, 0.2); }
+.icombo:hover .options { opacity: 1; }
+.icombo .option { display: block; padding: 4px 6px; }
+.icombo .option:hover { background: #4af; color: white; }
 </style>
 </head>
 <body>
diff --git a/main.js b/main.js
index dd8d059..fe0a67b 100644
--- a/main.js
+++ b/main.js
@@ -11,7 +11,7 @@ class Calc extends preact.Component
         afr_host: 5,
         capacity: 8,
         speed: 20,
-        pg_per_osd: 50,
+        pg_per_osd: 100,
         ec: false,
         replicas: 2,
         ec_data: 2,
@@ -19,6 +19,7 @@ class Calc extends preact.Component
         eager: false,
         same_host: true,
         result: 0,
+        use_speed: true,
     }
 
     calc(st)
@@ -30,7 +31,8 @@ class Calc extends preact.Component
             afr_drive: st.afr_drive/100,
             afr_host: st.afr_host/100,
             capacity: st.capacity*1000,
-            speed: st.speed/1000,
+            speed: st.use_speed ? st.speed/1000 : null,
+            disk_heal_hours: st.use_speed ? null : st.disk_heal_hours,
             ec: st.ec,
             ec_data: st.ec_data,
             ec_parity: st.ec_parity,
@@ -38,6 +40,7 @@ class Calc extends preact.Component
             pgs: st.pg_per_osd,
             osd_rm: !st.same_host,
             degraded_replacement: st.eager,
+            down_out_interval: 600,
         });
         this.setState(st);
     }
@@ -69,6 +72,16 @@ class Calc extends preact.Component
         this.calc({ eager: event.target.checked });
     }
 
+    useSpeed = () =>
+    {
+        this.calc({ use_speed: true, speed: this.state.speed || 20 });
+    }
+
+    useTime = () =>
+    {
+        this.calc({ use_speed: false, disk_heal_hours: 12 });
+    }
+
     setSameHost = (event) =>
     {
         this.calc({ same_host: event.target.checked });
@@ -110,7 +123,7 @@ class Calc extends preact.Component
                 Калькулятор вероятности отказа кластера Ceph/Vitastor
             </h2>
             <p>
-                Вероятность полного отказа кластера зависит от числа серверов и дисков
+                Вероятность потери данных в кластере зависит от числа серверов и дисков
                 (чем их больше, тем вероятность больше), от схемы избыточности, скорости ребаланса (восстановления),
                 и, конечно, непосредственно вероятности выхода из строя самих дисков и серверов.
             </p>
@@ -154,11 +167,23 @@ class Calc extends preact.Component
                     <td><input type="text" value={state.ec_parity} onchange={this.setter('ec_parity')} /></td>
                 </tr> : null}
                 <tr>
-                    <th>Оценочная скорость<br />восстановления на 1 OSD</th>
-                    <td><input type="text" value={state.speed} onchange={this.setter('speed')} /> МБ/с</td>
+                    <th>
+                        {state.use_speed ? 'Оценочная' : 'Оценочное'}&nbsp;
+                        <span className="icombo">
+                            {state.use_speed ? 'скорость' : 'время'} <span className="icon-arw-down"></span>
+                            <span className="options">
+                                <span className="option" onClick={this.useSpeed}>скорость</span>
+                                <span className="option" onClick={this.useTime}>время</span>
+                            </span>
+                        </span>
+                        <br />восстановления на 1 OSD
+                    </th>
+                    {state.use_speed
+                        ? <td><input type="text" value={state.speed} onchange={this.setter('speed')} /> МБ/с</td>
+                        : <td><input type="text" value={state.disk_heal_hours} onchange={this.setter('disk_heal_hours')} /> час(ов)</td>}
                 </tr>
                 <tr>
-                    <th><abbr title="Среднее число уникальных групп чётности (пар/троек и т.п.), включающих каждый отдельный диск. В Ceph нормой считается 100 PG на OSD, из которых, допустим, половина дублируется">PG на OSD</abbr></th>
+                    <th><abbr title="Среднее число уникальных групп чётности (пар/троек и т.п.), включающих каждый отдельный диск. В Ceph нормой считается 100 PG на OSD">PG на OSD</abbr></th>
                     <td><input type="text" value={state.pg_per_osd} onchange={this.setter('pg_per_osd')} /></td>
                 </tr>
                 <tr>