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Balance¶

This test needs at least 2 extra block devices, which can be separate (virtual) disks or partitions of the same disk.
Create a raid0 device from 1 x 5Gb disks:

 # mkfs.btrfs -d raid0 -m raid0 /dev/vdb 
 # mount /dev/vdb /mnt/raid
 # df -h | grep raid
 /dev/vdb        5.0G  3.4M  4.8G   1% /mnt/raid

check statistics:

 # btrfs filesystem df /mnt/raid 
Data, RAID0: total=512.00MiB, used=64.00KiB
Data, single: total=512.00MiB, used=256.00KiB
System, RAID0: total=8.00MiB, used=0.00B
System, single: total=32.00MiB, used=16.00KiB
Metadata, RAID0: total=256.00MiB, used=112.00KiB
Metadata, single: total=256.00MiB, used=0.00B
GlobalReserve, single: total=3.25MiB, used=0.00B
WARNING: Multiple block group profiles detected, see 'man btrfs(5)'.
WARNING:   Data: single, raid0
WARNING:   Metadata: single, raid0
WARNING:   System: single, raid0

create a big binary file

 # time dd if=/dev/random of=/mnt/raid/bigfile.bin bs=4M count=1024
1024+0 records in
1024+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 46.4441 s, 92.5 MB/s

real    0m46.445s
user    0m0.000s
sys 0m45.580s

check statistics to see disk usage

 # btrfs device usage  /mnt/raid/
/dev/vdb, ID: 1
   Device size:             5.00GiB
   Device slack:              0.00B
   Data,single:             3.94GiB
   Data,RAID0/1:          512.00MiB
   Metadata,single:       256.00MiB
   Metadata,RAID0/1:      256.00MiB
   System,single:          32.00MiB
   System,RAID0/1:          8.00MiB
   Unallocated:            21.00MiB

notice the difference between free space reported by 'df' and unallocated space reported by btrfs:

 # df -h | grep -E '(raid|Filesystem)'
Filesystem      Size  Used Avail Use% Mounted on
/dev/vdb        5.0G  4.1G  470M  90% /mnt/raid

# btrfs filesystem df  /mnt/raid/
Data, RAID0: total=512.00MiB, used=448.50MiB
Data, single: total=3.94GiB, used=3.56GiB
System, RAID0: total=8.00MiB, used=0.00B
System, single: total=32.00MiB, used=16.00KiB
Metadata, RAID0: total=256.00MiB, used=4.33MiB
Metadata, single: total=256.00MiB, used=0.00B
GlobalReserve, single: total=3.80MiB, used=0.00B
WARNING: Multiple block group profiles detected, see 'man btrfs(5)'.
WARNING:   Data: single, raid0
WARNING:   Metadata: single, raid0
WARNING:   System: single, raid0

now add a new disk device to the raid0:

 # btrfs device add -f /dev/vdc /mnt/raid/
 # btrfs device usage /mnt/raid/
/dev/vdb, ID: 1
   Device size:             5.00GiB
   Device slack:              0.00B
   Data,single:             3.94GiB
   Data,RAID0/1:          512.00MiB
   Metadata,single:       256.00MiB
   Metadata,RAID0/1:      256.00MiB
   System,single:          32.00MiB
   System,RAID0/1:          8.00MiB
   Unallocated:            21.00MiB

/dev/vdc, ID: 2
   Device size:             5.00GiB
   Device slack:              0.00B
   Unallocated:             5.00GiB

the aggregate filesystem now is larger, but the available space does not reflect the new size, because the filesystem is *unbalanced * ; we need to trigger balance of the filesytem. The next operation is I/O intensive :

# df -h | grep -E '(raid|Filesystem)'
Filesystem      Size  Used Avail Use% Mounted on
/dev/vdb         10G  4.1G  490M  90% /mnt/raid

# btrfs balance start --full-balance -v /mnt/raid 

now free space is available:

# df -h | grep raid
Filesystem      Size  Used Avail Use% Mounted on
/dev/vdb         10G  3.6G  6.3G  37% /mnt/raid

Here we can either force the balance, or just "start" it and let run in background, using the script in the maintenance package called /usr/share/btrfsmaintenance/btrfs-balance.sh

Acceptance Criteria¶

• AC1: BTRFS balance test is scheduled in Staging and product in development for SLES and ALP
• AC2: A good performance baseline is established, so we know when a bug or other defect hinders the performance.

Notes¶

• Contact the Kernel team to ask for an isci disc or similar with 100GB or better 1TB for these tests to be ran
• See documentation for backends at: https://github.com/os-autoinst/os-autoinst/blob/master/doc/backend_vars.asciidoc
• The objective is to test the functionality of the balance tools provided by the package rather than testing the tool from a performance perspective; we're looking to avoid scenarios where tests are failing due to
• stability of the test is proven by scheduling multiple test runs with different disk types and configurations, preferably using disks attached over the network via Netapp or something similar.