[Gluster-users] Disastrous performance with rsync to mounted Gluster volume.

[Ernie Dunbar]

On 2015-04-27 14:09, Joe Julian wrote:
> 
> I've also noticed that if I increase the count of those writes, the
> transfer speed increases as well:
> 
> 2097152 bytes (2.1 MB) copied, 0.036291 s, 57.8 MB/s
> root at backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
> count=2048 bs=1024; sync
> 2048+0 records in
> 2048+0 records out
> 2097152 bytes (2.1 MB) copied, 0.0362724 s, 57.8 MB/s
> root at backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
> count=2048 bs=1024; sync
> 2048+0 records in
> 2048+0 records out
> 2097152 bytes (2.1 MB) copied, 0.0360319 s, 58.2 MB/s
> root at backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
> count=10240 bs=1024; sync
> 10240+0 records in
> 10240+0 records out
> 10485760 bytes (10 MB) copied, 0.127219 s, 82.4 MB/s
> root at backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
> count=10240 bs=1024; sync
> 10240+0 records in
> 10240+0 records out
> 10485760 bytes (10 MB) copied, 0.128671 s, 81.5 MB/s
> 
> This is correct, there is overhead that happens with small files and
> the smaller the file the less throughput you get. That said, since
> files are smaller you should get more files / second but less MB /
> second. I have found that when you go under 16k changing files size
> doesn't matter, you will get the same number of 16k files / second as
> you do 1 k files.
> 
>  The overhead happens regardless. You just notice it more when you're
> doing it a lot more frequently.


Well, it would be helpful to know what specifically rsync is trying to 
do when it's sitting there making overhead, and whether it's possible to 
tell rsync to avoid doing it, and just copy files instead (which it does 
quite quickly).

I suppose technically speaking, it's an rsync-specific question, but 
it's all about making rsync and glusterfs play nice, and we pretty much 
all need to know that!