samba - Oct 2003 - Tuning Linux/Samba for low latency w/ high i/o

Hi all,

I am attempting to tune a (RedHat 7.3) Linux box running samba 2.2.8a. This
application is serving files to PC clients via samba, and the PC clients are
uploading files to the server via ftp.

Now for the specifics...

These files are mpeg2 encoded video with bit rates ranging from 3Mbit/s -
20Mbit/s. When there is zero write activity against the disks I can kick off
multiple concurrent streams (wrong terminology, but what the office refers to
opening a mpeg over the network) to different PCs and the video plays without
issue. (I forgot to mention that minimum file size is 500MB.)

If I start an upload via samba/ftp while I am watching a stream the server seems
to buffer arround 100MB with no problem, at that point data is written to disk
and both the ftp upload and the stream pause for 5 seconds and then continue.

(This is output from vmstat streaming a video)
   procs                      memory    swap          io     system        cpu
 r  b  w   swpd   free   buff  cache  si  so    bi    bo   in    cs  us  sy  id
 0  0  0      0  59804 215000 691484   0   0     0     0 1110   226   0   1  99
 0  0  0      0  58776 215000 692512   0   0  1028     0 1158   234   1   0 100
 0  0  0      0  58776 215000 692512   0   0     0     0 1116   226   0   1  99
 0  0  0      0  57748 215000 693540   0   0  1028     0 1134   230   0   9  91
 0  0  0      0  57748 215000 693540   0   0     0     0 1134   228   0   1  99
 0  0  0      0  56720 215000 694568   0   0  1028     0 1126   224   0   0 100

(These two are examples of pauses)

 0  0  0      0   8588 215096 740216   0   0     0   188 4222  4848   0   4 96
 1  1  1      0   8568 215100 737652   0   0     0 23916 4175  4810   0   5 96
 0  0  0      0   9580 215100 739964   0   0  1028   732 2825  2753   0  16 84
 0  0  0      0   9584 215104 740092   0   0     0   220 5036  5036   0   4 96

 0  0  0      0 404192 215460 345348   0   0     0   188 4205  4811   0   3 97
 0  1  0      0 393496 215468 348440   0   0  1032 11968 3463  3183   1   6 94
 1  0  0      0 397652 215468 351916   0   0  1028  2132 4247  3678   0   5 95
 0  0  0      0 394508 215472 355064   0   0     0   188 4516  4674   0   5 95

This box is a 2.4GHz Xeon w/ 1GB of RAM. There are two 36GB SCSI disks with an
MD Raid 1 mirror across them for OS and Swap. The main storage system is 8
Western Digital 200GB IDE disks connected to a 3ware 7508 Raid controller
configured in Raid5.

How do I approach tuning this configuration. I can sacrifice upload speed, but I
absolutely have to eliminate stalls in the video streams.

Thanks in advance,
Max

On Thu, Oct 02, 2003 at 10:06:50AM +0800, Ow Mun Heng
wrote:
> >>stream pause for 5 seconds and then continue.
> 
> How can you tell from the vmstat output? how do you read it? I do note that
> the bi & b0 values are _much_ higher when you upload some stuffs. (esp
your
> b0 values)
I am watching the video stream and ftp upload on a separate PC, with a console
running vmstat on another.
> >>server seems to buffer arround 100MB with no problem,
> What is buffering around 100MB? is this the bi value? 
When I do the FTP upload, the ftp server is buffering arround 100MB (the total
isn't reflected in vmstat).

-Max

--
Max Clark <maxc at beast.clarksys.com>