Discussion:
ZFS compression question
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r***@public.gmane.org
2013-12-30 01:45:05 UTC
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Hi,

I have a newbie question. I have a pool which is a single drive /sda1

I have compression enabled on this drive. I know the compression ratio:

zfs get compressratio /ssd/mnt
NAME PROPERTY VALUE SOURCE
ssd/mnt compressratio 1.92x -

So, why does 'df' not show any extra space, and when I use 'zfs list',
REFER shows the same as used?

NAME USED AVAIL REFER MOUNTPOINT
ssd 97.6G 340G 31K /ssd
ssd/mnt 97.6G 340G 97.6G /ssd/mnt


My drive started with 450 GB (around) and still looks to have gained no
space:

df
ssd 355967104 0 355967104 0% /ssd
ssd/mnt 458289792 102322688 355967104 23% /ssd/mnt


If I have 97GB with 1.92x compression, surely disk space should be around
50GB, leaving 400GB free.

I must be missing something fundamental here... perhaps someone can explain?

Many thanks,

RW
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Emmanuel Anne
2013-12-30 07:51:56 UTC
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When did you enable compression ?
Because if you filled your drive until 92% and then enabled compression,
what was written before didn't change, just the remaining 5% and something
were compressed.
For df it's very unprecise with compression, and with zfs it's better to
leave more than 5% of free space if you don't want to risk a huge slowdown.
Post by r***@public.gmane.org
Hi,
I have a newbie question. I have a pool which is a single drive /sda1
zfs get compressratio /ssd/mnt
NAME PROPERTY VALUE SOURCE
ssd/mnt compressratio 1.92x -
So, why does 'df' not show any extra space, and when I use 'zfs list',
REFER shows the same as used?
NAME USED AVAIL REFER MOUNTPOINT
ssd 97.6G 340G 31K /ssd
ssd/mnt 97.6G 340G 97.6G /ssd/mnt
My drive started with 450 GB (around) and still looks to have gained no
df
ssd 355967104 0 355967104 0% /ssd
ssd/mnt 458289792 102322688 355967104 23% /ssd/mnt
If I have 97GB with 1.92x compression, surely disk space should be around
50GB, leaving 400GB free.
I must be missing something fundamental here... perhaps someone can explain?
Many thanks,
RW
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