Getting and understanding free and allocated space stats

[dpearcefl]

I'm trying to get my head wrapped around how to calculate disk space usage on a ZFS volume/dataset. There seems to be multiple ways to get disk information, some of which is before or after compression/deduplication but not specified.

For instance:

If I run "du -h -d 1 -A" I get the apparent or actual uncompressed file sizes. From the filesystem's point of view, not very interesting. From a user's perspective, with compression you can actually "use" more disk space than you actually have.

The GUI's "compression rate" and what comes out of "zdb -D dataset" I have found out can be wildly wrong when you have a file with a bunch of empty space.

So if a PHB asks "How fast is the NAS filling up?", how do I get meaningful stats like the following:

• What is the actual compression ratio? (space used on the disk / space of original file)
• How much is deduplication saving us? (space used on the disk / space of original files)

When you dump files onto an EXT4 file system, it is easy to calculate these numbers. On a ZFS file system, it seems complicated knowing where you stand free space wise and allocated disk space.

Thanks.

 

[dlavigne]

zfs get space | more gives a better indication of what is happening space-wise (rather than du). As for compression, the default of LZ4 compresses on the fly, but only when the data to be compressed benefits from compression.

 

[dpearcefl]

zpool get all | more also returns useful information.