![]() If compression has a significant impact on your software performance, please confirm it first by running a test job with and without compression and then contact us at We will help you minimise the impact of compression on your workflow or find other ways to help you manage your project storage. I/O intensive workloads may experience a significant performance drop. The extent of the effect, however, depends on the magnitude of I/O operations on the affected files. Favours access speed over compression efficiency.Įxperiments showed that I/O performance was definitely affected if a file was in a compressed state. Favours compression efficiency over access speed. Depending on the Scale version installed, files can be tagged with different algorithms.Ĭurrently supported compression libraries are: The default algorithm is the Zlib and will be shown on the misc attributes of a tagged file as “library z”. It is still marked for compression as the COMPRESSION misc attribute suggests, but because it's not fully compressed the illcompressed flag will be shown. Partially compressed and tagged for compression - When file is partially compressed (either because it was decompressed for access or the full compression didn’t finish). Uncompressed and untagged for compression (default) - as shown for the file FileA.txt above. In addition, a file will exhibit the flag illcompressed when the desired final state is not the achieved yet (fully compressed or uncompressed).Ī file that is fully compressed (not showing the flag illcompressed and having the misc attribute COMPRESSION ), if updated or appended data to, becomes automatically illcompressed and either needs to be re-compressed using the mmchattr -compression yes command or the mmrestripefile -z one (because it's already tagged for compression). The misc attributes will have or not have a COMPRESSION value, depending on if the file is or not tagged for compression. We can check those attributes with the mmlsattr command: $ mmlsattr -L FileA.txt ![]() States of a compressed fileĬompressed files on Scale filesystems can be in 4 different states depending on the extended attributes of the file when manipulated for compression. Be aware that if, in the process of decompression, the quota will be exceeded, an error message will be displayed And vice versa, if files are decompressed, fully or partially, quota usage will increase. Therefore, if files are compressed, quota usage will decrease. This will be the total counting against quotas as well. ![]() However, du commands will calculate the approximate usage of the file system as opposed to the uncompressed usage. ![]() Ls command will show files with their original sizes. This state means that the file is only partially compressed. If the command fails halfway through the file or is cancelled, the file will be marked as "illcompressed". This method (using the mmchattr command) acts similar to gzip/ gunzip commands where the file being targeted is compressed or decompressed on command invocation. Note: as at, the `mm` commands are not available by default, contact for assistance There are two methods for compressing and decompressing data: on-demand and deferred: On-Demand (synchronous) It is possible to change algorithms at any time for any file (we will cover that further ahead) when the compression is requested. As a default, the Zlib compression algorithm will be used, although depending on the version of the filesystem, additional ones might be added. In the future, it is intended that there will be some automatic process regularly compressing flagged files, but at this time, it is only done manually by the NeSI team for specific filesets identified as suitable for the compression or by the user manually on their own filesets.įor purposes of this Guide, we are going to focus on the user side and what the users can do. This can be done by the user (front end) or at the back end via a policy for example. The data will need to be re-compressed after it is used if you are to maintain it in the compressed state. It allows you to treat the data as if it were not compressed. This means that that data can be compressed and then used without first needing to decompress it, as the decompression happens automatically in the background without the need for commands. Spectrum Scale filesystems (previously GPFS) allow users to compress data (but not metadata) transparently on demand without the need to change metadata (file creation and modification dates, etc).
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