diff --git a/mon/upgrade-simple.js b/mon/upgrade-simple.js
new file mode 100755
index 00000000..114160dc
--- /dev/null
+++ b/mon/upgrade-simple.js
@@ -0,0 +1,141 @@
+#!/usr/bin/node
+// Upgrade tool for OSD units generated with make-osd.sh and make-osd-hybrid.js
+
+const fsp = require('fs').promises;
+
+upgrade_osd(process.argv[2]).catch(e =>
+{
+    console.error(e.message);
+    process.exit(1);
+});
+
+async function upgrade_osd(unit)
+{
+    if (!unit)
+        throw new Error('USAGE: '+process.argv[0]+' '+process.argv[1]+' /etc/systemd/system/vitastor-osd<NUMBER>.service');
+    let service_name = /^.*\/(vitastor-osd\d+)\.service$/.exec(unit);
+    if (!service_name)
+        throw new Error(unit+' is not a service named vitastor-osd<number>');
+    service_name = service_name[1];
+    // Parse the unit
+    const text = await fsp.readFile(unit, { encoding: 'utf-8' });
+    let cmd = /\nExecStart\s*=[^\n]+vitastor-osd\s*(([^\n&>\d]+|\\[ \t\r]*\n|\d[^>])+)/.exec(text);
+    if (!cmd)
+        throw new Error('Failed to extract ExecStart command from '+unit);
+    cmd = cmd[1].replace(/\\[ \t\r]*\n/g, '');
+    const options = {};
+    for (let i = 0; i < cmd.length-1; i += 2)
+    {
+        if (cmd[i].substr(0, 2) == '--')
+            options[cmd[i].substr(2)] = cmd[i+1];
+        else
+            i--;
+    }
+    if (!options['osd_num'] || !options['data_device'])
+        throw new Error('osd_num or data_device are missing in '+unit);
+    if (options['data_device'].substr(0, '/dev/disk/by-partuuid/'.length) != '/dev/disk/by-partuuid/' ||
+        options['meta_device'] && options['meta_device'].substr(0, '/dev/disk/by-partuuid/'.length) != '/dev/disk/by-partuuid/' ||
+        options['journal_device'] && options['journal_device'].substr(0, '/dev/disk/by-partuuid/'.length) != '/dev/disk/by-partuuid/')
+    {
+        throw new Error(
+            'data_device, meta_device and journal_device must begin with'+
+            ' /dev/disk/by-partuuid/ i.e. they must be GPT partitions identified by UUIDs'
+        );
+    }
+    // Stop and disable the service
+    system_or_die("systemctl disable --now "+service_name);
+    const j_o = BigInt(options['journal_offset'] || 0);
+    const m_o = BigInt(options['meta_offset'] || 0);
+    const d_o = BigInt(options['data_offset'] || 0);
+    const m_is_d = !options['meta_device'] || options['meta_device'] == options['data_device'];
+    const j_is_m = !options['journal_device'] || options['journal_device'] == options['meta_device'];
+    const j_is_d = (options['journal_device'] || options['meta_device'] || options['data_device']) == options['data_device'];
+    if (d_o < 4096 || j_o < 4096 || m_o < 4096)
+    {
+        // Resize data
+        let blk = BigInt(options['block_size'] || 128*1024);
+        let resize = {};
+        if (d_o < 4096 || m_is_d && m_o < 4096 && m_o < d_o || j_is_d && j_o < 4096 && j_o < d_o)
+        {
+            resize.new_data_offset = d_o+blk;
+            if (m_is_d && m_o < d_o)
+                resize.new_meta_offset = m_o+blk;
+            if (j_is_d && j_o < d_o)
+                resize.new_journal_offset = j_o+blk;
+        }
+        if (!m_is_d && m_o < 4096)
+        {
+            resize.new_meta_offset = m_o+4096n;
+            if (j_is_m && m_o < j_o)
+                resize.new_journal_offset = j_o+4096n;
+        }
+        if (!j_is_d && !j_is_m && j_o < 4096)
+            resize.new_journal_offset = j_o+4096n;
+        const resize_opts = Object.keys(resize).map(k => ` --${k} ${resize[k]}`).join('');
+        console.log('Resize options:'+resize_opts);
+        await system_or_die(
+            'vitastor-disk resize'+
+            Object.keys(options).map(k => ` --${k} ${options[k]}`).join('')+resize_opts
+        );
+        for (let k in resize)
+            options[k.substr(4)] = resize[k];
+    }
+    // Write superblock
+    const sb = JSON.stringify(options);
+    await system_or_die('vitastor-disk write-sb '+options['data_device'], sb);
+    if (!m_is_d)
+        await system_or_die('vitastor-disk write-sb '+options['meta_device'], sb);
+    if (!j_is_d && !j_is_m)
+        await system_or_die('vitastor-disk write-sb '+options['journal_device'], sb);
+    // Change partition type
+    fix_partition_type(options['data_device']);
+    if (!m_is_d)
+        fix_partition_type(options['meta_device']);
+    if (!j_is_d && !j_is_m)
+        fix_partition_type(options['journal_device']);
+    // Enable the new unit
+    system_or_die("systemctl enable --now vitastor-osd@"+options['osd_num']);
+}
+
+async function fix_partition_type(dev)
+{
+    const uuid = dev.replace(/^.*\//, '').toLowerCase();
+    const parent_dev = (await fsp.realpath(dev)).replace(/((\d)p|(\D))?\d+$/, '$2$3');
+    const pt = JSON.parse(await system_or_die('sfdisk --dump '+parent_dev+' --json')).partitiontable;
+    let script = 'label: gpt\n\n';
+    for (const part of pt.partitions)
+    {
+        if (part.uuid.toLowerCase() == uuid)
+            part.type = 'e7009fac-a5a1-4d72-af72-53de13059903';
+        script += part.node+': '+Object.keys(part).map(k => k == 'node' ? '' : k+'='+part[k]).filter(k => k).join(', ')+'\n';
+    }
+    await system_or_die('sfdisk '+dev.path, script);
+}
+
+async function system_or_die(cmd, input = '')
+{
+    let [ exitcode, stdout, stderr ] = await system(cmd, input);
+    if (exitcode != 0)
+        throw new Error(cmd+' failed: '+stderr);
+    return stdout;
+}
+
+async function system(cmd, input = '')
+{
+    if (options.debug)
+    {
+        process.stderr.write('+ '+cmd+(input ? " <<EOF\n"+input.replace(/\s*$/, '\n')+"EOF" : '')+'\n');
+    }
+    const cp = child_process.spawn(cmd, { shell: true });
+    let stdout = '', stderr = '', finish_cb;
+    cp.stdout.on('data', buf => stdout += buf.toString());
+    cp.stderr.on('data', buf => stderr += buf.toString());
+    cp.on('exit', () => finish_cb && finish_cb());
+    cp.stdin.write(input);
+    cp.stdin.end();
+    if (cp.exitCode == null)
+    {
+        await new Promise(ok => finish_cb = ok);
+    }
+    return [ cp.exitCode, stdout, stderr ];
+}