Am 2018-05-15 00:57, schrieb Dave Chinner:
On Mon, May 14, 2018 at 05:02:53PM -0500, Eric Sandeen wrote:
On 5/14/18 3:02 PM, Tarik Ceylan wrote:
> How can one reliably measure filesystem usage on partitions that were compiled with -m reflink=1 ?
> Here are some numbers i am measuring with df -h (on different partitions holding the same data):
> 7.7G of 36G (-b size=512 -m crc=0 )
> 8.6G of 36G (-b size=4096 -m crc=1 )
8x larger inodes will take 8x more space, but you didn't say how many
inodes you have allocated.
> 11G of 36G (-b size=1024 -m crc=1,reflink=1,rmapbt=1 -i sparse=1 )
> 32G of 864G (-b size=4096 -m crc=1,reflink=1 )
In that last case, you have a wildly different total fs size, so
probably
no fair comparison here either.
The reverse mapping btree also takes up space. You're turning too
many
knobs at once. ;)
Thanks,
here's a test in which i only compare reflink=0 to reflink=1, all other
variables being the same:
mkfs.xfs -f -m reflink=0 /dev/sdc4
meta-data=/dev/sdc4 isize=512 agcount=4, agsize=58687982
blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=0,
rmapbt=0, reflink=0
data = bsize=4096 blocks=234751926,
imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal log bsize=4096 blocks=114624, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
"df -h" shows a usage of 8.8G of 896G
mkfs.xfs -f -m reflink=1 /dev/sdc4
[output same as before except the reflink parameter]
15G of 896G
Also, we reserve a lot of space for reflink/rmapbt metadata that
isn't actually used, so you're not actually using any more space
than the "-b size=4096 -m crc=1" case. I have plans for hiding that
reservation from users so that we don't get questions like this....
That should resolve my confusion. Sorry to have bothered, but it's kind
of
an obvious question.
To get back to my original question - can i assume "df" to be a
reliable
way of measuring fs usage going forward (after the change you mention),
or will specialized tools be necessary as is the case with btrfs?
Tarik
Cheers,
Dave.
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