diff --git a/src/era/dump.rs b/src/era/dump.rs
index a72bd51..cc3a9b1 100644
--- a/src/era/dump.rs
+++ b/src/era/dump.rs
@@ -1,4 +1,3 @@
-use anyhow::anyhow;
 use std::fs::File;
 use std::io::BufWriter;
 use std::io::Write;
@@ -12,7 +11,7 @@ use crate::era::xml;
 use crate::io_engine::{AsyncIoEngine, IoEngine, SyncIoEngine};
 use crate::pdata::array::{self, ArrayBlock};
 use crate::pdata::array_walker::*;
-use crate::pdata::bitset::read_bitset;
+use crate::pdata::bitset::read_bitset_no_err;
 use crate::pdata::btree_walker::btree_to_map;
 
 //------------------------------------------
@@ -78,6 +77,7 @@ fn mk_context(opts: &EraDumpOptions) -> anyhow::Result<Context> {
     Ok(Context { engine })
 }
 
+// notify the visitor about the marked blocks only
 fn dump_writeset(
     engine: Arc<dyn IoEngine + Send + Sync>,
     out: &mut dyn MetadataVisitor,
@@ -85,27 +85,68 @@ fn dump_writeset(
     ws: &Writeset,
     repair: bool,
 ) -> anyhow::Result<()> {
-    let (bits, errs) = read_bitset(engine.clone(), ws.root, ws.nr_bits as usize, repair);
     // TODO: deal with broken writeset
-    if errs.is_some() {
-        return Err(anyhow!(
-            "errors in writeset of era {}: {}",
-            era,
-            errs.unwrap()
-        ));
-    }
+    let bits = read_bitset_no_err(engine.clone(), ws.root, ws.nr_bits as usize, repair)?;
 
     out.writeset_b(&ir::Writeset {
         era,
         nr_bits: ws.nr_bits,
     })?;
-    for b in 0..ws.nr_bits {
-        let wbit = ir::WritesetBit {
-            block: b,
-            value: bits.contains(b as usize).unwrap_or(false),
-        };
-        out.writeset_bit(&wbit)?;
+
+    // [begin, end) denotes the range of set bits.
+    let mut begin: u32 = 0;
+    let mut end: u32 = 0;
+    for (index, entry) in bits.as_slice().iter().enumerate() {
+        let mut n = *entry;
+
+        if n == u32::MAX {
+            end = std::cmp::min(end + 32, ws.nr_bits);
+            continue;
+        }
+
+        while n > 0 {
+            let zeros = n.trailing_zeros();
+            if zeros > 0 {
+                if end > begin {
+                    let m = ir::MarkedBlocks {
+                        begin,
+                        len: end - begin,
+                    };
+                    out.writeset_blocks(&m)?;
+                }
+                n >>= zeros;
+                end += zeros;
+                begin = end;
+            }
+
+            let ones = n.trailing_ones();
+            n >>= ones;
+            end = std::cmp::min(end + ones, ws.nr_bits);
+        }
+
+        // emit the range if it ends before the entry boundary
+        let endpos = ((index as u32) << 5) + 32;
+        if end < endpos {
+            if end > begin {
+                let m = ir::MarkedBlocks {
+                    begin,
+                    len: end - begin,
+                };
+                out.writeset_blocks(&m)?;
+            }
+            begin = endpos;
+            end = begin;
+        }
     }
+
+    if end > begin {
+        let m = ir::MarkedBlocks {
+            begin,
+            len: end - begin,
+        };
+        out.writeset_blocks(&m)?;
+    }
+
     out.writeset_e()?;
 
     Ok(())
@@ -164,7 +205,7 @@ pub fn dump(opts: EraDumpOptions) -> anyhow::Result<()> {
     } else {
         writer = Box::new(BufWriter::new(std::io::stdout()));
     }
-    let mut out = xml::XmlWriter::new(writer);
+    let mut out = xml::XmlWriter::new(writer, false);
 
     if opts.logical {
         dump_metadata_logical(ctx.engine, &mut out, &sb, opts.repair)
diff --git a/src/era/ir.rs b/src/era/ir.rs
index 0dc1342..947a4f6 100644
--- a/src/era/ir.rs
+++ b/src/era/ir.rs
@@ -17,9 +17,9 @@ pub struct Writeset {
 }
 
 #[derive(Clone)]
-pub struct WritesetBit {
-    pub block: u32,
-    pub value: bool,
+pub struct MarkedBlocks {
+    pub begin: u32,
+    pub len: u32,
 }
 
 #[derive(Clone)]
@@ -42,7 +42,7 @@ pub trait MetadataVisitor {
 
     fn writeset_b(&mut self, ws: &Writeset) -> Result<Visit>;
     fn writeset_e(&mut self) -> Result<Visit>;
-    fn writeset_bit(&mut self, wbit: &WritesetBit) -> Result<Visit>;
+    fn writeset_blocks(&mut self, blocks: &MarkedBlocks) -> Result<Visit>;
 
     fn era_b(&mut self) -> Result<Visit>;
     fn era_e(&mut self) -> Result<Visit>;
diff --git a/src/era/restore.rs b/src/era/restore.rs
index bbd05db..127abca 100644
--- a/src/era/restore.rs
+++ b/src/era/restore.rs
@@ -70,7 +70,8 @@ pub struct Restorer<'a> {
     writeset_builder: Option<ArrayBuilder<u64>>, // bitset
     current_writeset: Option<ir::Writeset>,
     era_array_builder: Option<ArrayBuilder<u32>>,
-    writeset_buf: (u32, u64), // (index in u64 array, value)
+    writeset_entry: u64,
+    entry_index: u32,
     in_section: Section,
 }
 
@@ -83,7 +84,8 @@ impl<'a> Restorer<'a> {
             writeset_builder: None,
             current_writeset: None,
             era_array_builder: None,
-            writeset_buf: (0, 0),
+            writeset_entry: 0,
+            entry_index: 0,
             in_section: Section::None,
         }
     }
@@ -170,8 +172,8 @@ impl<'a> MetadataVisitor for Restorer<'a> {
             return Err(anyhow!("not in superblock"));
         }
         self.writeset_builder = Some(ArrayBuilder::new(div_up(ws.nr_bits as u64, 64)));
-        self.writeset_buf.0 = 0;
-        self.writeset_buf.1 = 0;
+        self.entry_index = 0;
+        self.writeset_entry = 0;
         self.current_writeset = Some(ws.clone());
         self.in_section = Section::Writeset;
         Ok(Visit::Continue)
@@ -185,7 +187,7 @@ impl<'a> MetadataVisitor for Restorer<'a> {
         if let Some(mut builder) = self.writeset_builder.take() {
             if let Some(ws) = self.current_writeset.take() {
                 // push the trailing bits
-                builder.push_value(self.w, self.writeset_buf.0 as u64, self.writeset_buf.1)?;
+                builder.push_value(self.w, self.entry_index as u64, self.writeset_entry)?;
 
                 let root = builder.complete(self.w)?;
                 self.writesets.insert(
@@ -206,20 +208,47 @@ impl<'a> MetadataVisitor for Restorer<'a> {
         Ok(Visit::Continue)
     }
 
-    fn writeset_bit(&mut self, wbit: &ir::WritesetBit) -> Result<Visit> {
-        if wbit.value {
-            let index = wbit.block >> 6;
-            let mask = 1 << (wbit.block & 63);
-            if index == self.writeset_buf.0 {
-                self.writeset_buf.1 |= mask;
-            } else {
-                let builder = self.writeset_builder.as_mut().unwrap();
-                builder.push_value(self.w, self.writeset_buf.0 as u64, self.writeset_buf.1)?;
-                self.writeset_buf.0 = index;
-                self.writeset_buf.1 = mask;
-            }
+    fn writeset_blocks(&mut self, blocks: &ir::MarkedBlocks) -> Result<Visit> {
+        let first = blocks.begin;
+        let last = first + blocks.len - 1; // inclusive
+        let mut idx = first >> 6;
+        let last_idx = last >> 6; // inclusive
+        let builder = self.writeset_builder.as_mut().unwrap();
+
+        // emit the bufferred bits
+        if idx > self.entry_index {
+            builder.push_value(self.w, self.entry_index as u64, self.writeset_entry)?;
+            self.entry_index = idx;
+            self.writeset_entry = 0;
         }
 
+        // buffer the bits of the first entry
+        let bi_first = first & 63;
+        if idx == last_idx {
+            let bi_last = last & 63;
+            let mask = 1u64 << bi_last;
+            self.writeset_entry |= (mask ^ mask.wrapping_sub(1)) & (u64::MAX << bi_first);
+
+            return Ok(Visit::Continue);
+        }
+
+        self.writeset_entry |= u64::MAX << bi_first;
+
+        // emit the all-1 entries if necessary
+        while idx < last_idx {
+            builder.push_value(self.w, self.entry_index as u64, self.writeset_entry)?;
+            self.entry_index += 1;
+            self.writeset_entry = u64::MAX;
+            idx += 1;
+        }
+
+        // buffer the bits of the last entry
+        builder.push_value(self.w, self.entry_index as u64, self.writeset_entry)?;
+        let bi_last = last & 63;
+        let mask = 1u64 << bi_last;
+        self.entry_index += 1;
+        self.writeset_entry |= mask ^ mask.wrapping_sub(1);
+
         Ok(Visit::Continue)
     }
 
diff --git a/src/era/xml.rs b/src/era/xml.rs
index 4153a1f..7b54b79 100644
--- a/src/era/xml.rs
+++ b/src/era/xml.rs
@@ -11,12 +11,18 @@ use crate::xml::*;
 
 pub struct XmlWriter<W: Write> {
     w: Writer<W>,
+    compact: bool,
+    nr_blocks: u32,
+    emitted_blocks: u32,
 }
 
 impl<W: Write> XmlWriter<W> {
-    pub fn new(w: W) -> XmlWriter<W> {
+    pub fn new(w: W, compact: bool) -> XmlWriter<W> {
         XmlWriter {
             w: Writer::new_with_indent(w, 0x20, 2),
+            compact,
+            nr_blocks: 0,
+            emitted_blocks: 0,
         }
     }
 }
@@ -29,8 +35,10 @@ impl<W: Write> MetadataVisitor for XmlWriter<W> {
         elem.push_attribute(mk_attr(b"block_size", sb.block_size));
         elem.push_attribute(mk_attr(b"nr_blocks", sb.nr_blocks));
         elem.push_attribute(mk_attr(b"current_era", sb.current_era));
-
         self.w.write_event(Event::Start(elem))?;
+
+        self.nr_blocks = sb.nr_blocks;
+
         Ok(Visit::Continue)
     }
 
@@ -46,21 +54,55 @@ impl<W: Write> MetadataVisitor for XmlWriter<W> {
         elem.push_attribute(mk_attr(b"era", ws.era));
         elem.push_attribute(mk_attr(b"nr_bits", ws.nr_bits));
         self.w.write_event(Event::Start(elem))?;
+
+        self.emitted_blocks = 0;
+
         Ok(Visit::Continue)
     }
 
     fn writeset_e(&mut self) -> Result<Visit> {
+        if !self.compact {
+            for b in self.emitted_blocks..self.nr_blocks {
+                let tag = b"bit";
+                let mut elem = BytesStart::owned(tag.to_vec(), tag.len());
+                elem.push_attribute(mk_attr(b"block", b));
+                elem.push_attribute(mk_attr(b"value", "false"));
+                self.w.write_event(Event::Empty(elem))?;
+            }
+        }
         self.w
             .write_event(Event::End(BytesEnd::borrowed(b"writeset")))?;
         Ok(Visit::Continue)
     }
 
-    fn writeset_bit(&mut self, wbit: &WritesetBit) -> Result<Visit> {
-        let tag = b"bit";
-        let mut elem = BytesStart::owned(tag.to_vec(), tag.len());
-        elem.push_attribute(mk_attr(b"block", wbit.block));
-        elem.push_attribute(mk_attr(b"value", wbit.value));
-        self.w.write_event(Event::Empty(elem))?;
+    fn writeset_blocks(&mut self, blocks: &MarkedBlocks) -> Result<Visit> {
+        if self.compact {
+            let tag = b"marked";
+            let mut elem = BytesStart::owned(tag.to_vec(), tag.len());
+            elem.push_attribute(mk_attr(b"block_begin", blocks.begin));
+            elem.push_attribute(mk_attr(b"len", blocks.len));
+            self.w.write_event(Event::Empty(elem))?;
+        } else {
+            for b in self.emitted_blocks..blocks.begin {
+                let tag = b"bit";
+                let mut elem = BytesStart::owned(tag.to_vec(), tag.len());
+                elem.push_attribute(mk_attr(b"block", b));
+                elem.push_attribute(mk_attr(b"value", "false"));
+                self.w.write_event(Event::Empty(elem))?;
+            }
+
+            let end = blocks.begin + blocks.len;
+            for b in blocks.begin..end {
+                let tag = b"bit";
+                let mut elem = BytesStart::owned(tag.to_vec(), tag.len());
+                elem.push_attribute(mk_attr(b"block", b));
+                elem.push_attribute(mk_attr(b"value", "true"));
+                self.w.write_event(Event::Empty(elem))?;
+            }
+
+            self.emitted_blocks = end;
+        }
+
         Ok(Visit::Continue)
     }
 
@@ -139,7 +181,7 @@ fn parse_writeset(e: &BytesStart) -> Result<Writeset> {
     })
 }
 
-fn parse_writeset_bit(e: &BytesStart) -> Result<WritesetBit> {
+fn parse_writeset_bit(e: &BytesStart) -> Result<Option<MarkedBlocks>> {
     let tag = "bit";
     let mut block: Option<u32> = None;
     let mut value: Option<bool> = None;
@@ -153,9 +195,36 @@ fn parse_writeset_bit(e: &BytesStart) -> Result<WritesetBit> {
         }
     }
 
-    Ok(WritesetBit {
-        block: check_attr(tag, "block", block)?,
-        value: check_attr(tag, "value", value)?,
+    check_attr(tag, "block", block)?;
+    check_attr(tag, "value", value)?;
+
+    if let Some(true) = value {
+        Ok(Some(MarkedBlocks {
+            begin: block.unwrap(),
+            len: 1,
+        }))
+    } else {
+        Ok(None)
+    }
+}
+
+fn parse_writeset_blocks(e: &BytesStart) -> Result<MarkedBlocks> {
+    let tag = "marked";
+    let mut begin: Option<u32> = None;
+    let mut len: Option<u32> = None;
+
+    for a in e.attributes() {
+        let kv = a.unwrap();
+        match kv.key {
+            b"block_begin" => begin = Some(u32_val(&kv)?),
+            b"len" => len = Some(u32_val(&kv)?),
+            _ => return bad_attr(tag, kv.key),
+        }
+    }
+
+    Ok(MarkedBlocks {
+        begin: check_attr(tag, "block_begin", begin)?,
+        len: check_attr(tag, "len", len)?,
     })
 }
 
@@ -198,7 +267,14 @@ where
             _ => return Err(anyhow!("Parse error at byte {}", reader.buffer_position())),
         },
         Ok(Event::Empty(ref e)) => match e.name() {
-            b"bit" => visitor.writeset_bit(&parse_writeset_bit(e)?),
+            b"bit" => {
+                if let Some(b) = parse_writeset_bit(e)? {
+                    visitor.writeset_blocks(&b)
+                } else {
+                    Ok(Visit::Continue)
+                }
+            }
+            b"marked" => visitor.writeset_blocks(&parse_writeset_blocks(e)?),
             b"era" => visitor.era(&parse_era(e)?),
             _ => return Err(anyhow!("Parse error at byte {}", reader.buffer_position())),
         },
diff --git a/src/pdata/bitset.rs b/src/pdata/bitset.rs
index fcd0942..86352b9 100644
--- a/src/pdata/bitset.rs
+++ b/src/pdata/bitset.rs
@@ -2,10 +2,13 @@ use fixedbitset::FixedBitSet;
 use std::sync::{Arc, Mutex};
 
 use crate::io_engine::IoEngine;
+use crate::math::div_up;
 use crate::pdata::array::{self, ArrayBlock};
 use crate::pdata::array_walker::{ArrayVisitor, ArrayWalker};
 use crate::pdata::space_map::*;
 
+//------------------------------------------
+
 pub struct CheckedBitSet {
     bits: FixedBitSet,
 }
@@ -30,6 +33,8 @@ impl CheckedBitSet {
     }
 }
 
+//------------------------------------------
+
 struct BitsetVisitor {
     nr_bits: usize,
     bits: Mutex<CheckedBitSet>,
@@ -72,6 +77,55 @@ impl ArrayVisitor<u64> for BitsetVisitor {
     }
 }
 
+//------------------------------------------
+
+struct BitsetCollector {
+    bits: Mutex<FixedBitSet>,
+    nr_bits: usize,
+}
+
+impl BitsetCollector {
+    fn new(nr_bits: usize) -> BitsetCollector {
+        BitsetCollector {
+            bits: Mutex::new(FixedBitSet::with_capacity(nr_bits)),
+            nr_bits,
+        }
+    }
+
+    pub fn get_bitset(self) -> FixedBitSet {
+        self.bits.into_inner().unwrap()
+    }
+}
+
+impl ArrayVisitor<u64> for BitsetCollector {
+    fn visit(&self, index: u64, b: ArrayBlock<u64>) -> array::Result<()> {
+        let mut bitset = self.bits.lock().unwrap();
+        let mut idx = (index as usize * b.header.max_entries as usize) << 1; // index of u32 in bitset array
+        let idx_end = div_up(self.nr_bits, 32);
+        let mut dest = bitset.as_mut_slice().iter_mut().skip(idx);
+        for entry in b.values.iter() {
+            let lower = (*entry & (u32::MAX as u64)) as u32;
+            *(dest.next().ok_or_else(|| {
+                array::value_err(format!("bitset size exceeds limit: {} bits", self.nr_bits))
+            })?) = lower;
+            idx += 1;
+
+            if idx == idx_end {
+                break;
+            }
+
+            let upper = (*entry >> 32) as u32;
+            *(dest.next().ok_or_else(|| {
+                array::value_err(format!("bitset size exceeds limit: {} bits", self.nr_bits))
+            })?) = upper;
+            idx += 1;
+        }
+        Ok(())
+    }
+}
+
+//------------------------------------------
+
 // TODO: multi-threaded is possible
 pub fn read_bitset(
     engine: Arc<dyn IoEngine + Send + Sync>,
@@ -106,3 +160,15 @@ pub fn read_bitset_with_sm(
     };
     Ok((v.get_bitset(), e))
 }
+
+pub fn read_bitset_no_err(
+    engine: Arc<dyn IoEngine + Send + Sync>,
+    root: u64,
+    nr_bits: usize,
+    ignore_none_fatal: bool,
+) -> array::Result<FixedBitSet> {
+    let w = ArrayWalker::new(engine, ignore_none_fatal);
+    let mut v = BitsetCollector::new(nr_bits);
+    w.walk(&mut v, root)?;
+    Ok(v.get_bitset())
+}