[Samba] Very slow write performance to RAID

[Kevin Taylor]

We have a RAID set up as our main fileserver (running samba 3.0.33 on linux, CentOS 5). The main disk area is an XFS partition of about 8TB. I'm using iostat to monitor disk I/O since we've gotten complaints about speed and I'm noticing that when I write something to the samba share, the write speed is horrible. For a 15GB file it is reporting to finish in about 20 minutes.

iostat reports very little write I/O...on the level of maybe 7 write i/o's every 5 seconds or so.

If I were to read .5GB of data off of the samba share, it transfers quickly (and I see 300 reads/s through iostat)...which would be about normal.

Any idea of why I'm getting such lousy write speed? 

If generate some data to write on the fileserver itself (not going through samba) I can get some decent numbers.

With the command:   dd if=/dev/zero of=/data/testfile bs=1024k count=10000

I saw the 10GB write with a speed of 270MB/s, which is decent, so I'm not thinking there's anything wrong with the disk or raid controller.