File compression

Use this table to access IBM Spectrum Scale documentation for file compression and decompression.

Table 1. Quick reference for file compression and decompression
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Differences between file compression and object compression.	Comparison with object compression
The supported compression libraries are z, lz4, zfast, alphae, and alphah. They are intended primarily for compressing the following types of data: z Cold data. Favors compression efficiency over access speed. lz4 Active, non-specific data. Favors access speed over compression efficiency. zfast Active genomic data in FASTA, SAM, or VCF format. alphae Active genomic data in FASTQ format. Slightly favors compression efficiency over access speed. alphah Active genomic data in FASTQ format. Slightly favors access speed over compression efficiency.	File compression
Use one of the following commands to compress or decompress files: mmchattr mmapplypolicy with a MIGRATE COMPRESS rule	Setting up file compression and decompression mmchattr command mmapplypolicy command Policy rules: Syntax
Do not do any of the following operations while an mmrestorefs command is running: File compression or decompression with mmchattr or mmapplypolicy mmrestripefs or mmrestripefile	Warning
OS commands display the decompressed size.	Reported size of compressed files
You can defer file compression or decompression until the file system is not busy. Run mmrestorefs or mmrestorefile to complete the deferred operation.	Deferred file compression mmrestripefs command mmrestripefile command
COMPRESSION indicates whether the file is marked for compression or decompression. illCompressed indicates whether the compression or decompression is complete or deferred.	Indicators of file compression or decompression
Writing data to a compressed file decompresses the affected region of the file.	Updates to compressed files Partially compressed files
You can memory-map a file that is already compressed. File compression avoids compressing a memory-mapped file.	File compression and memory mapping
You can open a compressed file for Direct I/O, but internally the reads and writes are decompressed. File compression avoids compressing a file that is opened for Direct I/O.	File compression and direct I/O
Files are decompressed when they are moved out of storage that is directly managed by IBM Spectrum Scale. When you restore files to the IBM Spectrum Scale file system, you can run mmrestorefs or mmrestorefile to recompress the files.	Backing up and restoring compressed files
File compression supports a File Placement Optimizer (FPO) environment or horizontal storage pools.	FPO environment
Files that belong to AFM and AFM DR filesets can be compressed and decompressed.	AFM environment
No compression occurs if the space savings is less than 10 per cent. File compression is not supported in some environments. File compression with mmapplypolicy is not supported in Microsoft Windows.	Limitations