another question about zfs compression numbers

Eugene M. Zheganin eugene at zhegan.in
Wed Apr 4 07:46:38 UTC 2018


Hi,

On 04.04.2018 12:35, Patrick M. Hausen wrote:
> Hi all,
>
>> Am 04.04.2018 um 09:21 schrieb Eugene M. Zheganin <eugene at zhegan.in>:
>> I'm just trying to understand these numbers:
>>
>> file size is 232G, it's actual size on the lz4-compressed dataset is 18G, so then why is the compressratio only 1.86x ? And why logicalused is 34.2G ? On one hand, 34.2G exactlyfits to the 1.86x compresstaio, but still I don't get it. dataset is on raidz, 3 spans across 5 disk vdevs, with total of 15 disks if it matters:
> A sparse file, possibly? The ZFS numbers refer to blocks. "Skipping" zeroes at the
> VFS layer is not taken into account as fas as I know. Seriously, how should it?
> If I'm not mistaken, ZFS will never get to see these empty blocks.
>
Looks so, thanks. Although it's a mysql tablespace file. But yeah, in 
hex viewer looks like it's filled with zeroes in many places.

Eugene.



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