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 - It 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
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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 |
Deferred file compression:
- You can defer file compression or decompression until the file system is not busy.
- Run mmrestorefs or mmrestorefile to complete the deferred
operation.
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Compression parameters:
- The parameter COMPRESSION indicates whether the file is marked for
compression or decompression.
- The parameter 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. |
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Memory-mapping:
- You can memory-map a file that is already compressed.
- File compression avoids compressing a memory-mapped file.
|
File compression and memory mapping |
Direct I/O files:
- 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 |
File decompressing:
- 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 |
File compression does not occur in the following scenarios:
- 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.
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Limitations |