Large gluster read performance overhead?

[Raghuram BK <ram@xxxxxxxxxxxxx>]

I've been trying to figure out the performance overhead of gluster over the underlying filesystem and find the difference to be quite stark. Is this normal? Can something be done about it? I've tried to eliminate the network overhead by doing everything locally and eliminate the effect of caching by forcing hits to the hard drives.. Here's what I did :

1. Force the underlying filesystem(ZFS) to always read from disk

2. Create the underlying storage (zfs create frzpool/normal/d1)

3. Create a gluster distributed volume with only one brick on the local machine. (gluster volume create g1 fractalio-pri.fractalio.lan:/frzpool/normal/d1 force)

4. Start it (gluster volume start g1)

5. Check the volume info :

[root@fractalio-pri fractalio]# gluster v info g1
 
Volume Name: g1
Type: Distribute
Volume ID: e50f13d2-cb98-47f4-8113-3f15b4b6306a
Status: Started
Number of Bricks: 1
Transport-type: tcp
Bricks:
Brick1: fractalio-pri.fractalio.lan:/frzpool/normal/d1

6. Mount it (mount -t glusterfs localhost:/g1 /mnt/g1)

7. Populate a test file into the volume :

[root@fractalio-pri fractalio]# dd if=/dev/zero of=/mnt/g1/ddfile1 bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes (2.1 GB) copied, 8.4938 s, 247 MB/s

8. Read the file from the gluster mount :

[root@fractalio-pri fractalio]# dd if=/mnt/g1/ddfile1 of=/dev/zero bs=1M
2000+0 records in
2000+0 records out
2097152000 bytes (2.1 GB) copied, 84.4174 s, 24.8 MB/s

9. Read the file directly from the underlying storage :

[root@fractalio-pri fractalio]# dd if=/frzpool/normal/d1/ddfile1 of=/dev/zero bs=1M
2000+0 records in
2000+0 records out
2097152000 bytes (2.1 GB) copied, 24.722 s, 84.8 MB/s

The throughput comes down from 84.8MB/s to 24.8MB/s, a 240% overhead?!

_______________________________________________
Gluster-users mailing list
Gluster-users@xxxxxxxxxxx
http://www.gluster.org/mailman/listinfo/gluster-users