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In getting and formatting 2 X 4tb WD green drives by "mkfs.btrfs -m raid1 -d raid1 /dev/sdc /dev/sdd" and then mount by "mount /dev/sdc /mnt" each drive if filled half the size of a copied file -- raid 0 behavior. I find this even more odd because when I run "btrfs fi df /mnt" it prints the following:
Data, RAID1: total=3.00GiB, used=2.51GiB
System, RAID1: total=32.00MiB, used=16.00KiB
Metadata, RAID1: total=1.00GiB, used=3.03MiB
GlobalReserve, single: total=16.00MiB, used=0.00
"btrfs fi show /mnt" prints
Label: none uuid: 4a7536a5-14ea-4f8a-8fe1-672d666f6cbb
Total devices 2 FS bytes used 2.52GiB
devid 1 size 3.64TiB used 4.03GiB path /dev/sdc
devid 2 size 3.64TiB used 4.03GiB path /dev/sdd
and gparted shows each drive as having used ~1.26GB. What is going on?
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Measuring the space used/free in btrfs is very tricky and the output often is a little misleading.
I have about 900GB of space total in a RAID1 configuration with four disks of various mixed sizes. I currently have about 50GB left free and am using LZO compression.
Here are various outputs for comparison:
# btrfs fi df /
Data, RAID1: total=445.00GiB, used=414.60GiB
System, RAID1: total=32.00MiB, used=72.00KiB
Metadata, RAID1: total=2.00GiB, used=1.08GiB
GlobalReserve, single: total=372.00MiB, used=0.00# btrfs fi show /
Label: 'removed' uuid: 98xxaxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
Total devices 4 FS bytes used 415.74GiB
devid 1 size 153.38GiB used 151.03GiB path /dev/sda
devid 2 size 74.53GiB used 73.00GiB path /dev/sdb
devid 3 size 232.89GiB used 231.00GiB path /dev/sdc
devid 4 size 465.76GiB used 439.03GiB path /dev/sdd# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda 485786196 436330996 67668432 87% /Note how 'btrfs fi show /' shows the actual physical space whereas 'btrfs fi df /' shows roughly half the amount as the data is RAID1.
Could some of the seeming discrepancy be due to compression in use on the file?
Last edited by davidm (2014-10-25 05:04:27)
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Nope, maximally compressed by lzop, file size decreases by 8MB to 2.69GB. The file has to be split across drives.
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According to http://lwn.net/Articles/577961/ it may be the case that gparted cannot be trusted to show accurate file system usage. I'm going to have to ask the gparted guys.
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gparted is not being well maintained it appears in regards to btrfs. I suppose this should be withdrawn? I'm not used to tools not working.
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