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Re: Compression effectiveness?

PeteMoran
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Compression effectiveness?

We use a RN104 (which replaced a standalone companion PC) to save Windows Image backups and database file dumps before transfer offsite.

 

The Windows system images were quite compressible using NTFS compression.

 

The database file dumps were highly compressible.

 

For example;

 

A 333,520,896 byte file gives the following results;

 

NTFS 126,586,880

ZIP 57,962,496

BZ2 48,298,874

 

As near as I can tell, unless there is another method of checking (used 'ls -l' from ssh), the ReadyNAS on-disk size is 333,170,328, barely 1% saving and hardly worth the effort.

 

Consequently, the client is not getting the historic file saving ability we expected.

 

Are our expectations too high? Firmware is 6.2.4.

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StephenB
Guru

Re: Compression effectiveness?

https://btrfs.wiki.kernel.org/index.php/Compression#How_can_I_determine_compressed_size_of_a_file.3F

 

Based on the wiki link, I think you need to do a df before and after compression.

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StephenB
Guru

Re: Compression effectiveness?

https://btrfs.wiki.kernel.org/index.php/Compression#How_can_I_determine_compressed_size_of_a_file.3F

 

Based on the wiki link, I think you need to do a df before and after compression.

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PeteMoran
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Re: Compression effectiveness?

Thank you. Great reference.

 

Looks like our files might suffer from "if the first portion of data being compressed is not smaller than the original, the compression of the file is disabled" because the df -k result shows ~72,810kbytes if force compression is on.

 

Seems like the compress decision is made on the first 4k block of data for the file.

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