diff --git a/zimmer.js b/zimmer.js
index 9b016da..2144c1b 100755
--- a/zimmer.js
+++ b/zimmer.js
@@ -394,48 +394,33 @@ class Cluster {
     // <2nd Blob>          data        n/a     n/a     data of the <2nd Blob>
     // ...                 data        ...     n/a     ...
 
-    async save () {
+    async getData () {
         //~ log( 'Cluster.prototype.save', this.compressible, this.blobs )
 
-        var nBlobs = this.blobs.length
-        if ( nBlobs == 0 )
-            return Promise.resolve()
-
         // generate blob offsets
-        var offsets = Buffer.alloc(( nBlobs + 1 ) * 4 )
-        var blobOffset = offsets.length
-        for ( var i=0; i < nBlobs; i++ ) {
-            offsets.writeUIntLE( blobOffset, i * 4, 4 )
-            blobOffset += this.blobs[ i ].length
-        }
-        //~ log( this.id,'generate blob offsets', nBlobs, offsets.length, i, blobOffset )
-        offsets.writeUIntLE( blobOffset, i * 4, 4 ) // final offset
+        const byteLength = 4
+        let blobOffset = ( this.blobs.length + 1 ) * byteLength
+        const offsetIndex = this.blobs.map(( blob, i, arr ) => {
+            const val = [ blobOffset, byteLength ]
+            blobOffset += blob.length
+            return val
+        })
+        offsetIndex.push([ blobOffset, byteLength ]) // final offset
 
-        // join offsets and article data
-        this.blobs.unshift( offsets )
-        var data = Buffer.concat( this.blobs )
-        var rawSize = data.length
+        const chunks = offsetIndex.concat( this.blobs )
 
-        var compression = this.compressible ? 4 : 0
-        var id = this.id
+        let data = chunksToBuffer( chunks )
 
-        if ( compression ) {
+        if ( this.compressible ) {
             // https://tukaani.org/lzma/benchmarks.html
-            data = await lzma.compress( data, 7 ) // 3 | lzma.PRESET_EXTREME )
+            // https://catchchallenger.first-world.info/wiki/Quick_Benchmark:_Gzip_vs_Bzip2_vs_LZMA_vs_XZ_vs_LZ4_vs_LZO
+            data = await lzma.compress( data, 5 ) // 3 | lzma.PRESET_EXTREME )
             log( 'Cluster lzma compressed' )
         }
+        
+        const compression = toBuffer( this.compressible ? 4 : 0, 1 )
 
-        log( 'Cluster write', id, compression )
-        const offset = await out.write( Buffer.concat([ Buffer.from([ compression ]), data ]))
-
-        log( 'Cluster saved', id, offset )
-        return wikiDb.run(
-            'INSERT INTO clusters (id, offset) VALUES (?,?)',
-            [
-                id,
-                offset
-            ]
-        )
+        return Buffer.concat([ compression, data ])
     }
 }
 
@@ -445,6 +430,7 @@ class Cluster {
 class ClusterPool {
     constructor () {
         this.holder = {}
+        this.savePrefix = outPath + '.tmp'
         this.pool = genericPool.createPool(
             {
                 create () { return Promise.resolve( Symbol() ) },
@@ -465,25 +451,37 @@ class ClusterPool {
         return cluster
     }
 
-    async append ( mimeType, data, id /* for debugging */ ) {
-        //~ log( 'ClusterWriter.append', arguments )
+    async save ( cluster ) {
+        const data = await cluster.getData()
+        await fs.outputFile( osPath.join( this.savePrefix, `${cluster.id}` ), data )
+        await wikiDb.run(
+            'INSERT INTO clusters ( id, size ) VALUES ( ?,? )',
+            [
+                cluster.id,
+                data.length
+            ]
+        )
+        log( 'Cluster saved', cluster.id, data.length )
+        return
+    }
 
-        var compressible = this.isCompressible( mimeType, data, id )
+    async append ( mimeType, data, path /* for debugging */ ) {
+        var compressible = this.isCompressible( mimeType, data, path )
         var cluster = this.getCluster( compressible )
         var clusterNum = cluster.id
         var blobNum = cluster.append( data )
 
-        if ( blobNum === false ) { // store to a new cluster
+        if ( blobNum === false ) { // save current cluster, create and store into a new cluster
             this.removeCluster( compressible )
             const token = await this.pool.acquire()
 
-            cluster.save()
-            .then( () => this.pool.release( token ))
+            await this.save( cluster )
+            this.pool.release( token )
 
-            return this.append( mimeType, data, id )
+            return this.append( mimeType, data, path )
         }
 
-        log( 'ClusterWriter.append', compressible, clusterNum, blobNum, data.length, id )
+        log( 'ClusterWriter.append', compressible, clusterNum, blobNum, data.length, path )
         return [ clusterNum, blobNum ]
     }
 
@@ -508,31 +506,51 @@ class ClusterPool {
     // ...     integer     ...     8   ...
 
     async storeIndex () {
+        const byteLength = 8
+        const count = header.clusterCount
+        const start = await out.write( Buffer.alloc( 0 ))
+        let offset = start + count * byteLength
+        
         header.clusterPtrPos = await saveIndex ({
-            query:
-                'SELECT ' +
-                    'offset ' +
-                'FROM clusters ' +
-                'ORDER BY id ' +
-                ';',
-            byteLength: 8,
-            count: header.clusterCount,
+            query:`
+                SELECT 
+                    size 
+                FROM clusters 
+                ORDER BY id 
+                ;`,
+            rowField: 'size',
+            byteLength,
+            count,
             logPrefix: 'storeClusterIndex',
             rowCb: ( row, index ) => {
-                return row.offset
+                const val = offset
+                offset += row.size
+                return val
             },
-
         })
     }
 
+    async storeClusters () {
+        for ( let i = 0; i < header.clusterCount; i++ ) {
+            const fname = osPath.join( this.savePrefix, `${i}` )
+            const data = await fs.readFile( fname )
+            const pos = await out.write( data )
+            log( 'storeClusters', i, pos )
+            await fs.remove( fname )
+        }
+        await fs.remove( this.savePrefix )
+    }
+
     async finish () {
         //~ log( 'ClusterWriter.finish', ClusterWriter )
         for ( let i in this.holder ) { // save last clusters
-            await this.holder[ i ].save()
+            await this.save( this.holder[ i ] )
         }
         await this.pool.drain()
         await this.pool.clear()
-        return this.storeIndex()
+        await this.storeIndex()
+        await this.storeClusters()
+        return
     }
 }
 
@@ -1121,7 +1139,7 @@ async function openWikiDb( dbName ) {
             );
         CREATE TABLE clusters (
             id INTEGER PRIMARY KEY,
-            offset INTEGER
+            size INTEGER
             );
         `
     )
@@ -1520,11 +1538,12 @@ async function loadRawArticles () {
 }
 
 async function postProcess () {
-    await clusterWriter.finish()
     await sortArticles()
     await resolveRedirects()
     await storeUrlIndex()
-    return storeTitleIndex()
+    await storeTitleIndex()
+    await clusterWriter.finish()
+    return
 }
 
 async function finalise () {