Hallo, Hugo,
Du meintest am 09.04.11:
>> df /srv/MM
>> btrfs filesystem df /srv/MM
>>
>> show some completely wrong values:
>>
>> # df /srv/MM
>>
>> Filesystem 1K-blocks Used Available Use% Mounted on
>> /dev/sdd1 5846053400 1593436456 2898463184 36% /srv/MM
>>
>> # btrfs filesystem df /srv/MM
>>
>> Data, RAID0: total=1.67TB, used=1.48TB
>> System, RAID1: total=16.00MB, used=112.00KB
>> System: total=4.00MB, used=0.00
>> Metadata, RAID1: total=3.75GB, used=2.26GB
>>
>> # btrfs-show
>>
>> Label: MMedia uuid: 120b036a-883f-46aa-bd9a-cb6a1897c8d2
>> Total devices 3 FS bytes used 1.48TB
>> devid 3 size 1.81TB used 573.76GB path /dev/sdb1
>> devid 2 size 1.81TB used 573.77GB path /dev/sde1
>> devid 1 size 1.82TB used 570.01GB path /dev/sdd1
>>
>> Btrfs Btrfs v0.19
>>
>> ------------------------------------------------
>>
>> "df" shows an "Available" value which isn't related to any real
>> value.
> I _think_ that value is the amount of space not allocated to any
> block group. If that's so, then Available (from df) plus the three
> "total" values (from btrfs fi df) should equal the size value from
> df.
I'm not convinced - sorry.
"used" plus "available" should be nearly the same value as the "total"
in "df"; in my example 1.6 TB + 2.9 TB is far away from the total of 5.8
TB (here: Tera = 10^9).
> The total value in the output of "btrfs fi df" is the total space
> allocated to block groups. As the filesystem needs more space, it
> will allocate more block groups from the available raw storage pool,
> and the number will go up.
> This is explained on the wiki at [1].
I've studied the page - the data shown there looks to be consistent.
Especially: "used" plus "avail" = "size"
-------------------------------------
The data seems (mostly) to be consistent on a new array of disks/
partitions. But when I work with "device add" and "device delete" then
there are holes.
Another machine:
/dev/sda about 140 GB
/dev/sdb about 140 GB
/dev/sdc about 70 GB
# mkfs.btrfs -L SCSI -d raid0 -m raid1 /dev/sdb1 /dev/sdc1
# mit 70 GByte gefüllt
# df -t btrfs
Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/sdb1 btrfs 214058944 73956996 65522124 54% /mnt/SCSI
# btrfs filesystem show
Label: 'SCSI' uuid: 1932d11d-021a-4054-8429-db25a0204221
Total devices 2 FS bytes used 70.43GB
devid 1 size 136.73GB used 37.03GB path /dev/sdb1
devid 2 size 67.41GB used 37.01GB path /dev/sdc1
# btrfs filesystem df /mnt/SCSI
Data, RAID0: total=72.00GB, used=70.33GB
Data: total=8.00MB, used=0.00
System, RAID1: total=8.00MB, used=12.00KB
System: total=4.00MB, used=0.00
Metadata, RAID1: total=1.00GB, used=104.78MB
Metadata: total=8.00MB, used=0.00
#------------------------------------------------------------
# btrfs device add /dev/sda1 /mnt/SCSI
# df -t btrfs
Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/sdb1 btrfs 356234160 84177056 200667344 30% /mnt/SCSI
# btrfs filesystem show
Label: 'SCSI' uuid: 1932d11d-021a-4054-8429-db25a0204221
Total devices 3 FS bytes used 80.16GB
devid 1 size 136.73GB used 42.03GB path /dev/sdb1
devid 3 size 135.59GB used 0.00 path /dev/sda1
devid 2 size 67.41GB used 42.01GB path /dev/sdc1
# btrfs filesystem df /mnt/SCSI
Data, RAID0: total=82.00GB, used=80.04GB
Data: total=8.00MB, used=0.00
System, RAID1: total=8.00MB, used=12.00KB
System: total=4.00MB, used=0.00
Metadata, RAID1: total=1.00GB, used=119.54MB
Metadata: total=8.00MB, used=0.00
#------------------------------------------------------------
# btrfs fi balance /mnt/SCSI
# df -t btrfs
Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/sdb1 btrfs 356234160 84125344 228211536 27% /mnt/SCSI
# btrfs filesystem show
Label: 'SCSI' uuid: 1932d11d-021a-4054-8429-db25a0204221
Total devices 3 FS bytes used 80.14GB
devid 1 size 136.73GB used 28.28GB path /dev/sdb1
devid 3 size 135.59GB used 27.00GB path /dev/sda1
devid 2 size 67.41GB used 29.01GB path /dev/sdc1
# btrfs filesystem df /mnt/SCSI
Data, RAID0: total=81.00GB, used=80.04GB
Data: total=8.00MB, used=0.00
System, RAID1: total=8.00MB, used=12.00KB
System: total=4.00MB, used=0.00
Metadata, RAID1: total=1.25GB, used=94.29MB
Metadata: total=8.00MB, used=0.00
#------------------------------------------------------------
# btrfs device delete /dev/sdc1 /mnt/SCSI
# umount /mnt/SCSI
# mount LABEL=SCSI /mnt/SCSI
# df -t btrfs
Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/sdb1 btrfs 285548192 232024076 51758540 82% /mnt/SCSI
# btrfs filesystem show
Label: 'SCSI' uuid: 1932d11d-021a-4054-8429-db25a0204221
Total devices 2 FS bytes used 221.04GB
devid 1 size 136.73GB used 111.51GB path /dev/sdb1
devid 3 size 135.59GB used 111.51GB path /dev/sda1
# btrfs filesystem df /mnt/SCSI
Data, RAID0: total=222.00GB, used=220.80GB
System, RAID1: total=8.00MB, used=24.00KB
System: total=4.00MB, used=0.00
Metadata, RAID1: total=512.00MB, used=243.77MB
--------------------------------------------------------------
What "df" shows as "available" immediately after creation is wrong.
What it shows after "device add" is wrong.
What it shows after "balance" is wrong.
What it shows after "device delete" looks ok.
Ok - now I presume that sometimes "df" or/and the "btrfs" commands only
show wrong values, but the system works with the right values (there ist
more free space than shown). But I fear that's not reliable.
--------------------------------
I also write scripts etc; I know since decades it's easy to make
mistakes, but sometimes it's hard work to find them.
Viele Gruesse!
Helmut
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