#bioinformatics #fasta #compression


Better FASTA sequence compression and querying

2 releases

0.3.4 Dec 19, 2022
0.3.3 Oct 25, 2022

#147 in Biology

29 downloads per month
Used in sfasta





Sfasta is a replacement for the FASTA/Q format with a goal of both saving space but also having very fast random-access for machine learning, even for large datasets (such as the nt database, 217Gb gzip compressed, 225Gb bgzip compressed, and 175Gb with sfasta, including an index).

Speed comes from assuming modern hardware, thus:

  • Multiple compression threads
  • I/O dedicated threads
  • SIMD bitpacking support
  • modern compression algorithms (ZSTD, as default).
  • Dual level ID Index
  • Everything stored as sequence streams (for better compression).

If you need different hardware support, open an issue. There are SIMD support for other architectures that could be implemented.

While the goals are random-access speed by ID query, and smaller size, I hope it can become a more general purpose format. It supports other compression algorithms, which could be used for archival purposes (such as xz compression). This is a work in progress, but ready for community feedback. Because the goals are not simple decompression, this part of the code is not-optimized yet, and is much slower than zcat and other tools. This will be remedied in the future.


This has taken a few years of on again, off again development. FORMAT.md and other files are likely out of date.

Community Feedback Period

I'm hopeful folks will check this out, play around, break it, and give feedback.

FASTQ support

It's now trivial to add the scores as another compression stream, and the struct that puts it all back together already has an entries for scores. I'll get to it soon.


  • Does Zstd dict support work for small block sizes (8kb, 16kb, 4kb)?
  • less than 8kbp block sizes should use dicts by default
  • Masking as bitvec or [Bool; N]?



cargo install sfasta Don't have cargo?


To compress a file:

sfa convert MyFile.fasta

You can also convert directly from gzipped files:

sfa convert MyFile.fasta.gz

You can use other compression schemes. The software automatically detects which is used and decompresses accordingly.

sfa convert --snappy MyFile.fasta sfa convert --xz MyFile.fasta

You can also change the block size. Units are in * 1024 bytes. Default is 4Mb (4096):

sfa convert --block-size 8192 MyFile.fasta

View a file:

sfa view MyFile.sfasta

Query a file by sequence ID:

sfa faidx MyFile.sfasta Chr1

For help:

sfa --help

Please note, not all subcommands are implemented yet. The following should work: convert, view, list, faidx.


Should work anywhere that supports Rust. Tested on Ubuntu, Red Hat, and Windows 10. I suspect it will work on Mac OS. I also do not think it supports WASM at this time.



Compression Type Random Access Multithreaded
sfasta Yes Yes
bgzip Yes Yes

Uniprot Random Access

Samtools index pre-built

Command Mean [ms] Min [ms] Max [ms] Relative
sfa faidx uniprot_sprot.sfasta "sp|Q6GZX1|004R_FRG3G" 123.8 ± 4.5 121.8 143.7 1.00
samtools faidx uniprot_sprot.fasta.gz "sp|Q6GZX1|004R_FRG3G" 423.0 ± 3.3 419.4 434.1 3.42 ± 0.13

Uniprot Compression Speed

Command Mean [s] Min [s] Max [s] Relative
sfa convert uniprot_sprot.fasta 1.974 ± 0.128 1.673 2.143 5.75 ± 0.59
ennaf --protein uniprot_sprot.fasta --temp-dir /tmp 0.923 ± 0.009 0.913 0.942 2.69 ± 0.22
bgzip -k --index -f --threads 8 uniprot_sprot.fasta 0.670 ± 0.019 0.641 0.734 1.95 ± 0.17
pigz -k -p 8 uniprot_sprot.fasta -f 0.636 ± 0.021 0.612 0.682 1.85 ± 0.16
crabz -p 8 Erow_1.0.fasta -f > uniprot_sprot.crabz 9.150 ± 0.182 8.883 9.523 26.67 ± 2.20
zstd -k uniprot_sprot.fasta -f -T8 0.343 ± 0.027 0.296 0.406 1.00

Uniprot Size

Uncompressed: 282M

Compression Type Size
sfasta (index incl) 83M
NAF (no index) 68M
zstd (no index) 78M
bgzip (excl. indexx) 92M

Nanopore Reads

As a FASTA file.

Nanopore Reads Compression Speed

Command Mean [s] Min [s] Max [s] Relative
sfa convert nanopore.fasta 22.844 ± 2.973 18.514 26.591 3.37 ± 0.45
ennaf nanopore.fasta --temp-dir /tmp 19.231 ± 0.158 19.003 19.505 2.84 ± 0.10
bgzip -k --index -f --threads 7 nanopore.fasta 82.065 ± 0.478 81.559 82.720 12.10 ± 0.42
pigz -k -p 7 nanopore.fasta -f 83.118 ± 0.994 82.055 85.015 12.26 ± 0.44
crabz -p 7 nanopore.fasta > nanopore.fasta.crabz 82.933 ± 1.268 81.313 84.412 12.23 ± 0.46
zstd -k nanopore.fasta -f -T7 6.780 ± 0.232 6.484 7.220 1.00

Nanopore Reads Random Access

Samtools index pre-built

Command Mean [ms] Min [ms] Max [ms] Relative
sfa faidx nanopore.sfasta ae278260-d941-45c9-9e76-40f04ef8e56c 83.6 ± 10.6 71.7 98.5 1.00
samtools faidx nanopore.fasta.gz ae278260-d941-45c9-9e76-40f04ef8e56c 752.6 ± 5.8 746.7 764.8 9.01 ± 1.15

Nanopore Reads Size

Uncompressed Size: 8.8G

Compression Type Size
NAF (no index) 2.2G
sfasta (incl index) 2.6G
bgzip (excl index) 2.6G
zstd (no index) 2.7G


Genome Random Access Speed

Samtools index pre-built

Command Mean [ms] Min [ms] Max [ms] Relative
sfa faidx Erow_1.0.sfasta PXIH01S0167520.1 135.3 ± 9.4 129.4 153.4 1.09 ± 0.09
samtools faidx Erow_1.0.fasta.gz PXIH01S0167520.1 189.7 ± 10.2 182.2 215.7 1.53 ± 0.10

Genome Compression Speed

Command Mean [s] Min [s] Max [s] Relative
sfa convert Erow_1.0.fasta 4.847 ± 0.189 4.579 5.199 2.39 ± 0.16
ennaf Erow_1.0.fasta --temp-dir /tmp 8.054 ± 0.044 7.986 8.155 3.97 ± 0.22
bgzip -k --index -f --threads 10 Erow_1.0.fasta 7.522 ± 0.510 6.639 8.132 3.71 ± 0.32
pigz -k -p 10 Erow_1.0.fasta -f 7.593 ± 0.110 7.353 7.965 3.75 ± 0.21
crabz -p 10 Erow_1.0.fasta > Erow_1.0.crabz 7.530 ± 0.203 7.317 7.992 3.72 ± 0.23
zstd -k Erow_1.0.fasta -f -T10 2.026 ± 0.112 1.834 2.273 1.00

Genome Size

Uncompressed: 2.7G

Compression Type Size
NAF (no index) 446M
sfasta (incl index) 596M
bgzip (excl index) 635M
Zstd (no index) 663M

Future Plans

Implement NAF-like algorithm

NAF has an advantage with 4bit encoding. It's possible to implement this, and use 2bit when possible, to gain additional speed-ups. Further, there is some SIMD support for 2bit and 4bit DNA/RNA encoding.

Subsequence support for faidx CLI

Only open the block(s) that contain the subsequence. The index is already set up to support this and I've had it working before in the python bindings.

Additional Speed-ups

There is plenty of room for speed improvements, including adding more threads for specific tasks, CPU affinities, native compilation, and maybe more Cow.

Additional Compression

There is likely room to decrease size as well without hurting speed.

Command-line interface

As I've refactored much of the library, the CLI code withered and decayed. Need to fix this.

Quality Scores

To support FASTQ files

Adjust compression level and compression method

For other applications (such as long term storage)

C and Python bindings

To make it easier to use in other programs and in python/jupyter

Small file optimization

Sfasta is currently optimized for larger files.

GFA file format support

Graph genome file format is in dire need of an optimized format

Profile Guided Optimization

Never mind. This somehow doubled the time it takes to compress binaries. Enable PGO for additional speed-ups


The following format parsers are fuzzed. To fuzz execute the following in the libsfasta directory:

cargo fuzz run parse_fastq  -- -max_len=8388608
cargo fuzz run parse_fasta  -- -max_len=8388608
cargo fuzz run parse_sfasta -- -detect_leaks=0 -rss_limit_mb=4096mb -max_len=8388608


I get a strange symbol near the progress bar

You need to install a font that supports Unicode. I'll see if there is a way to auto-detect.

XZ compression is fast until about halfway, then slows to a crawl.

The buffers can store lots of sequence, but the compression algorithm takes longer.

Why so many dependencies?

Right it it works with a wide range of compression functions. Once some are determined to be the best others could be dropped from future versions. The file format itself has a version identifier so we could request people rollback to an older version if they need to.

Why samtools comparison?

I've got plenty of experiments trying to get a fast gzip compressed multi-threaded reader, but even when mounted on a ramdisk, it is too slow. Samtools is an awesome, handy tool that has the 'faidx' function, of which I am a huge fan. While the faidx is not it's main function, it is not optimized for large datasets, thus the test is a little unfair. Still, it's helpful to have something to compare to.

File Format

The best source is currently this file: conversion.rs. Masking is converted into instructions in a u32, see ml32bit.rs.


Data Type Name Description
[u8; 6] b"sfasta" Indicates an sfasta file
u64 Version Version of the SFASTA file (currently set to 1)
struct Directory Directory of the file; u64 bytes pointing to indices, sequence blocks, etc...
struct Parameters Parameters used to create the file
struct Metadata unused
structs SequenceBlock Sequences, split into block_size chunks, and compressed on disk (see: SequenceBlockCompressed)
Vec Sequence Block Offsets Location of each sequence block, in bytes, from the start of the file. Stored on disk as bitpacked u32.
Header Region
enum CompressionType Type of compression used for the Headers.
u64 Block Locations Position Position of the header blocks locations
[u8] Header Block Header (everything after the sequence ID in a FASTA file) stored as blocks of u8 on disk, zstd compressed.
[u64] Header Block Offsets Location of each header block, in bytes, from the start of the file.
IDs Region
enum CompressionType Type of compression used for the IDs.
u64 Block Locations Position Position of the ID blocks locations
[u8] ID Block IDs (everything after the sequence ID in a FASTA file) stored as blocks of u8 on disk, zstd compressed.
[u64] ID Block Offsets Location of each header block, in bytes, from the start of the file.
Masking Region
u64 bitpack_len Length of each bitpacked block
u8 num_bits Number of bits used to bitpack each integer
[Packed] BitPacked Masking Instructions Bitpacked masking instructions. See here
[struct] SeqLocs Sequence locations, stored as a vector of u64.
Special Dual Index See file for more description. Rest of this table TBD

Genomics Aotearoa


~440K SLoC