[Gluster-devel] Arbiter brick size estimation

[Oleksandr Natalenko]

In order to estimate GlusterFS arbiter brick size, I've deployed test setup 
with replica 3 arbiter 1 volume within one node. Each brick is located on 
separate HDD (XFS with inode size == 512). Using GlusterFS v3.7.6 + memleak 
patches. Volume options are kept default.

Here is the script that creates files and folders in mounted volume: [1]

The script creates 1M of files of random size (between 1 and 32768 bytes) and 
some amount of folders. After running it I've got 1036637 folders. So, in 
total it is 2036637 files and folders.

The initial used space on each brick is 42M . After running script I've got:

replica brick 1 and 2: 19867168 kbytes == 19G
arbiter brick: 1872308 kbytes == 1.8G

The amount of inodes on each brick is 3139091. So here goes estimation.

Dividing arbiter used space by files+folders we get:

(1872308 - 42000)/2036637 == 899 bytes per file or folder

Dividing arbiter used space by inodes we get:

(1872308 - 42000)/3139091 == 583 bytes per inode

Not sure about what calculation is correct. I guess we should consider the one 
that accounts inodes because of .glusterfs/ folder data.

Nevertheless, in contrast, documentation [2] says it should be 4096 bytes per 
file. Am I wrong with my calculations?

Pranith?

[1] http://termbin.com/ka9x
[2] http://gluster.readthedocs.org/en/latest/Administrator%20Guide/arbiter-volumes-and-quorum/