diff --git a/mon/make-osd-hybrid.js b/mon/make-osd-hybrid.js
new file mode 100755
index 000000000..487f80df9
--- /dev/null
+++ b/mon/make-osd-hybrid.js
@@ -0,0 +1,414 @@
+#!/usr/bin/nodejs
+// systemd unit generator for hybrid (HDD+SSD) vitastor OSDs
+// Copyright (c) Vitaliy Filippov, 2019+
+// License: VNPL-1.1
+
+// USAGE: nodejs make-osd-hybrid.js [--disable_ssd_cache 0] [--disable_hdd_cache 0] /dev/sda /dev/sdb /dev/sdc /dev/sdd ...
+// I.e. - just pass all HDDs and SSDs mixed, the script will decide where
+// to put journals on its own
+
+const fs = require('fs');
+const fsp = fs.promises;
+const child_process = require('child_process');
+
+const options = {
+    debug: 1,
+    journal_size: 1024*1024*1024,
+    min_meta_size: 1024*1024*1024,
+    object_size: 1024*1024,
+    bitmap_granularity: 4096,
+    device_block_size: 4096,
+    disable_ssd_cache: 1,
+    disable_hdd_cache: 1,
+};
+
+run().catch(console.fatal);
+
+async function run()
+{
+    const device_list = parse_options();
+    await system_or_die("mkdir -p /var/log/vitastor; chown vitastor /var/log/vitastor");
+    // Collect devices
+    const all_devices = await collect_devices(device_list);
+    const ssds = all_devices.filter(d => d.ssd);
+    const hdds = all_devices.filter(d => !d.ssd);
+    // Collect existing OSD units
+    const osd_units = await collect_osd_units();
+    // Count assigned HDD journals and unallocated space for each SSD
+    await check_journal_count(ssds, osd_units);
+    // Create new OSDs
+    await create_new_hybrid_osds(hdds, ssds, osd_units);
+    process.exit(0);
+}
+
+function parse_options()
+{
+    const devices = [];
+    const opt = {};
+    for (let i = 2; i < process.argv.length; i++)
+    {
+        const arg = process.argv[i];
+        if (arg == '--help' || arg == '-h')
+        {
+            opt.help = true;
+            break;
+        }
+        else if (arg.substr(0, 2) == '--')
+            opt[arg.substr(2)] = process.argv[++i];
+        else
+            devices.push(arg);
+    }
+    if (opt.help || !devices.length)
+    {
+        console.log(
+            'Prepare hybrid (HDD+SSD) Vitastor OSDs\n'+
+            '(c) Vitaliy Filippov, 2019+, license: VNPL-1.1\n\n'+
+            'USAGE: nodejs make-osd-hybrid.js [OPTIONS] /dev/sda /dev/sdb /dev/sdc ...\n'+
+            'Just pass all your SSDs and HDDs in any order, the script will distribute OSDs for you.\n\n'+
+            'OPTIONS (with defaults):\n'+
+            Object.keys(options).map(k => `  --${k} ${options[k]}`).join('\n')
+        );
+        process.exit(0);
+    }
+    for (const k in opt)
+        options[k] = opt[k];
+    return devices;
+}
+
+// Collect devices
+async function collect_devices(devices_to_check)
+{
+    const devices = [];
+    for (const dev of devices_to_check)
+    {
+        if (dev.substr(0, 5) != '/dev/')
+        {
+            console.log(`${dev} does not start with /dev/, skipping`);
+            continue;
+        }
+        if (!await file_exists('/sys/block/'+dev.substr(5)))
+        {
+            console.log(`${dev} is a partition, skipping`);
+            continue;
+        }
+        // Check if the device is an SSD
+        const rot = '/sys/block/'+dev.substr(5)+'/queue/rotational';
+        if (!await file_exists(rot))
+        {
+            console.log(`${dev} does not have ${rot} to check whether it's an SSD, skipping`);
+            continue;
+        }
+        const ssd = !parseInt(await fsp.readFile(rot, { encoding: 'utf-8' }));
+        // Check if the device has partition table
+        let [ has_partition_table, parts ] = await system(`sfdisk --dump ${dev} --json`);
+        if (has_partition_table != 0)
+        {
+            // Check if the device has any data
+            const [ has_data, out ] = await system(`blkid ${dev}`);
+            if (has_data == 0)
+            {
+                console.log(`${dev} contains data, skipping:\n  ${out.trim().replace(/\n/g, '\n  ')}`);
+                continue;
+            }
+        }
+        parts = parts ? JSON.parse(parts).partitiontable : null;
+        if (parts && parts.label != 'gpt')
+        {
+            console.log(`${dev} contains "${parts.label}" partition table, only GPT is supported, skipping`);
+            continue;
+        }
+        devices.push({
+            path: dev,
+            ssd,
+            parts,
+        });
+    }
+    return devices;
+}
+
+// Collect existing OSD units
+async function collect_osd_units()
+{
+    const units = [];
+    for (const unit of (await system("ls /etc/systemd/system/vitastor-osd*.service"))[1].trim().split('\n'))
+    {
+        if (!unit)
+        {
+            continue;
+        }
+        let cmd = /^ExecStart\s*=\s*(([^\n]*\\\n)*[^\n]*)/.exec(await fsp.readFile(unit, { encoding: 'utf-8' }));
+        if (!cmd)
+        {
+            console.log('ExecStart= not found in '+unit+', skipping')
+            continue;
+        }
+        let kv = {}, key;
+        cmd = cmd[1].replace(/^bash\s+-c\s+'/, '')
+            .replace(/>>\s*\S+2>\s*&1\s*'$/, '')
+            .replace(/\s*\\\n\s*/g, ' ')
+            .replace(/([^\s']+)|'([^']+)'/g, (m, m1, m2) =>
+            {
+                m1 = m1||m2;
+                if (key == null)
+                {
+                    if (m1.substr(0, 2) != '--')
+                    {
+                        console.log('Strange command line in '+unit+', stopping');
+                        process.exit(1);
+                    }
+                    key = m1.substr(2);
+                }
+                else
+                {
+                    kv[key] = m1;
+                    key = null;
+                }
+            });
+        units.push(kv);
+    }
+    return units;
+}
+
+// Count assigned HDD journals and unallocated space for each SSD
+async function check_journal_count(ssds, osd_units)
+{
+    const units_by_journal = osd_units.reduce((a, c) =>
+    {
+        if (c.journal_device)
+            a[c.journal_device] = c;
+        return a;
+    }, {});
+    for (const dev of ssds)
+    {
+        dev.journals = 0;
+        if (dev.parts)
+        {
+            for (const part of dev.parts.partitions)
+            {
+                if (part.uuid && units_by_journal['/dev/disk/by-partuuid/'+part.uuid.toLowerCase()])
+                {
+                    dev.journals++;
+                }
+            }
+            dev.free = free_from_parttable(dev.parts);
+        }
+        else
+        {
+            dev.free = parseInt(await system_or_die("blockdev --getsize64 "+dev.path));
+        }
+    }
+}
+
+async function create_new_hybrid_osds(hdds, ssds, osd_units)
+{
+    const units_by_disk = osd_units.reduce((a, c) => { a[c.data_device] = c; return a; }, {});
+    for (const dev of hdds)
+    {
+        if (!dev.parts)
+        {
+            // HDD is not partitioned yet, create a single partition
+            // + is the "default value" for sfdisk
+            await system_or_die('sfdisk '+dev.path, 'label: gpt\n\n+ +\n');
+            dev.parts = JSON.parse(await system_or_die('sfdisk --dump '+dev.path+' --json')).partitiontable;
+        }
+        if (dev.parts.partitions.length != 1)
+        {
+            console.log(dev.path+' has more than 1 partition, skipping');
+        }
+        else if ((dev.parts.partitions[0].start + dev.parts.partitions[0].size) != (1 + dev.parts.lastlba))
+        {
+            console.log(dev.path+'1 is not a whole-disk partition, skipping');
+        }
+        else if (!dev.parts.partitions[0].uuid)
+        {
+            console.log(dev.parts.partitions[0].node+' does not have UUID. Please repartition '+dev.path+' with GPT');
+        }
+        else if (!units_by_disk['/dev/disk/by-partuuid/'+dev.parts.partitions[0].uuid.toLowerCase()])
+        {
+            await create_hybrid_osd(dev, ssds);
+        }
+    }
+}
+
+async function create_hybrid_osd(dev, ssds)
+{
+    // Create a new OSD
+    // Calculate metadata size
+    const data_device = '/dev/disk/by-partuuid/'+dev.parts.partitions[0].uuid.toLowerCase();
+    const data_size = dev.parts.partitions[0].size * dev.parts.sectorsize;
+    const meta_entry_size = 24 + 2*options.object_size/options.bitmap_granularity/8;
+    const entries_per_block = Math.floor(options.device_block_size / meta_entry_size);
+    const object_count = Math.floor(data_size / options.object_size);
+    let meta_size = Math.ceil(1 + object_count / entries_per_block) * options.device_block_size;
+    // Leave some extra space for future metadata formats and round metadata area size to multiples of 1 MB
+    meta_size = 2*meta_size;
+    meta_size = Math.ceil(meta_size/1024/1024) * 1024*1024;
+    if (meta_size < options.min_meta_size)
+        meta_size = options.min_meta_size;
+    let journal_size = Math.ceil(options.journal_size/1024/1024) * 1024*1024;
+    // Pick an SSD for journal, balancing the number of journals across SSDs
+    let selected_ssd;
+    for (const ssd of ssds)
+        if (ssd.free >= (meta_size+journal_size) && (!selected_ssd || selected_ssd.journals > ssd.journals))
+            selected_ssd = ssd;
+    if (!selected_ssd)
+    {
+        console.error('Could not find free space for SSD journal and metadata for '+dev.path);
+        process.exit(1);
+    }
+    // Allocate an OSD number
+    const osd_num = (await system_or_die("vitastor-cli alloc-osd")).trim();
+    if (!osd_num)
+    {
+        console.error('Failed to run vitastor-cli alloc-osd');
+        process.exit(1);
+    }
+    console.log('Creating OSD '+osd_num+' on '+dev.path+' (HDD) with journal and metadata on '+selected_ssd.path+' (SSD)');
+    // Add two partitions: journal and metadata
+    const new_parts = await add_partitions(selected_ssd, [ journal_size, meta_size ]);
+    selected_ssd.journals++;
+    const journal_device = '/dev/disk/by-partuuid/'+new_parts[0].uuid.toLowerCase();
+    const meta_device = '/dev/disk/by-partuuid/'+new_parts[1].uuid.toLowerCase();
+    // Wait until the device symlinks appear
+    while (!await file_exists(journal_device))
+    {
+        await new Promise(ok => setTimeout(ok, 100));
+    }
+    while (!await file_exists(meta_device))
+    {
+        await new Promise(ok => setTimeout(ok, 100));
+    }
+    // Zero out metadata and journal
+    await system_or_die("dd if=/dev/zero of="+journal_device+" bs=1M count="+(journal_size/1024/1024)+" oflag=direct");
+    await system_or_die("dd if=/dev/zero of="+meta_device+" bs=1M count="+(meta_size/1024/1024)+" oflag=direct");
+    // Create unit file for the OSD
+    const has_scsi_cache_type = options.disable_ssd_cache &&
+        (await system("ls /sys/block/"+selected_ssd.path.substr(5)+"/device/scsi_disk/*/cache_type"))[0] == 0;
+    const write_through = options.disable_ssd_cache && (
+        has_scsi_cache_type || selected_ssd.path.substr(5, 4) == 'nvme'
+        && (await system_or_die("/sys/block/"+selected_ssd.path.substr(5)+"/queue/write_cache")).trim() == "write through");
+    await fsp.writeFile('/etc/systemd/system/vitastor-osd'+osd_num+'.service',
+`[Unit]
+Description=Vitastor object storage daemon osd.${osd_num}
+After=network-online.target local-fs.target time-sync.target
+Wants=network-online.target local-fs.target time-sync.target
+PartOf=vitastor.target
+
+[Service]
+LimitNOFILE=1048576
+LimitNPROC=1048576
+LimitMEMLOCK=infinity
+ExecStart=bash -c '/usr/bin/vitastor-osd \\
+    --osd_num ${osd_num} ${write_through
+        ? "--disable_meta_fsync 1 --disable_journal_fsync 1 --immediate_commit "+(options.disable_hdd_cache ? "all" : "small")
+        : ""} \\
+    --throttle_small_writes 1 \\
+    --disk_alignment ${options.device_block_size} \\
+    --journal_block_size ${options.device_block_size} \\
+    --meta_block_size ${options.device_block_size} \\
+    --journal_no_same_sector_overwrites true \\
+    --journal_sector_buffer_count 1024 \\
+    --block_size ${options.object_size} \\
+    --data_device ${data_device} \\
+    --journal_device ${journal_device} \\
+    --meta_device ${meta_device} >>/var/log/vitastor/osd${osd_num}.log 2>&1'
+WorkingDirectory=/
+ExecStartPre=+chown vitastor:vitastor ${data_device}
+ExecStartPre=+chown vitastor:vitastor ${journal_device}
+ExecStartPre=+chown vitastor:vitastor ${meta_device}${
+    has_scsi_cache_type
+    ? "\nExecStartPre=+bash -c 'D=$$$(readlink "+journal_device+"); echo write through > $$$(dirname /sys/block/*/$$\${D##*/})/device/scsi_disk/*/cache_type'"
+    : ""}${
+    options.disable_hdd_cache
+    ? "\nExecStartPre=+bash -c 'D=$$$(readlink "+data_device+"); echo write through > $$$(dirname /sys/block/*/$$\${D##*/})/device/scsi_disk/*/cache_type'"
+    : ""}
+User=vitastor
+PrivateTmp=false
+TasksMax=infinity
+Restart=always
+StartLimitInterval=0
+RestartSec=10
+
+[Install]
+WantedBy=vitastor.target
+`);
+    await system_or_die("systemctl enable vitastor-osd"+osd_num);
+}
+
+async function add_partitions(dev, sizes)
+{
+    let script = 'label: gpt\n\n';
+    if (dev.parts)
+    {
+        // Old partitions
+        for (const part of dev.parts.partitions)
+        {
+            script += part.node+': '+Object.keys(part).map(k => k == 'node' ? '' : k+'='+part[k]).filter(k => k).join(', ')+'\n';
+        }
+    }
+    // New partitions
+    for (const size of sizes)
+    {
+        script += '+ '+Math.ceil(size/1024)+'KiB\n';
+    }
+    await system_or_die('sfdisk '+dev.path, script);
+    // Get new partition table and find the new partition
+    const newpt = JSON.parse(await system_or_die('sfdisk --dump '+dev.path+' --json')).partitiontable;
+    const old_nodes = dev.parts ? dev.parts.partitions.reduce((a, c) => { a[c.uuid] = true; return a; }, {}) : {};
+    const new_nodes = newpt.partitions.filter(part => !old_nodes[part.uuid]);
+    if (new_nodes.length != sizes.length)
+    {
+        console.error('Failed to partition '+dev.path+': new partitions not found in table');
+        process.exit(1);
+    }
+    dev.parts = newpt;
+    dev.free = free_from_parttable(newpt);
+    return new_nodes;
+}
+
+function free_from_parttable(pt)
+{
+    let free = pt.lastlba + 1 - pt.firstlba;
+    for (const part of pt.partitions)
+    {
+        free -= part.size;
+    }
+    free *= pt.sectorsize;
+    return free;
+}
+
+async function system_or_die(cmd, input = '')
+{
+    let [ exitcode, stdout, stderr ] = await system(cmd, input);
+    if (exitcode != 0)
+    {
+        console.error(cmd+' failed: '+stderr);
+        process.exit(1);
+    }
+    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 ];
+}
+
+async function file_exists(filename)
+{
+    return new Promise((ok, no) => fs.access(filename, fs.constants.R_OK, err => ok(!err)));
+}
diff --git a/mon/simple-offsets.js b/mon/simple-offsets.js
index dd9337764..e2ae667db 100644
--- a/mon/simple-offsets.js
+++ b/mon/simple-offsets.js
@@ -49,7 +49,8 @@ async function run()
     }
     options.journal_offset = Math.ceil(options.journal_offset/options.device_block_size)*options.device_block_size;
     const meta_offset = options.journal_offset + Math.ceil(options.journal_size/options.device_block_size)*options.device_block_size;
-    const entries_per_block = Math.floor(options.device_block_size / (24 + 2*options.object_size/options.bitmap_granularity/8));
+    const meta_entry_size = 24 + 2*options.object_size/options.bitmap_granularity/8;
+    const entries_per_block = Math.floor(options.device_block_size / meta_entry_size);
     const object_count = Math.floor((device_size-meta_offset)/options.object_size);
     const meta_size = Math.ceil(1 + object_count / entries_per_block) * options.device_block_size;
     const data_offset = meta_offset + meta_size;