[Samba] Samba 3 write performance drop on files > 16 MB

[DKrause at jw.org]

> I have been running performance tests on our Debian-Samba 3 file
> server.  It is running the 2.4 kernel on a ProLiant DL380 G3 server
> (Full Specs below).  For a windows client, we are running Windows 2003
> server on the exact same hardware.  They are both running at Gigabit
> speed.  
> 
> What we have found is that on files 16MB and smaller we can get better
> performance Windows client to Linux Server through SMB than we can get
> Windows to local disk.  (Both servers have the same disk subsystem)
> We get around 120,000KB/sec throughput.  But after 16MB, the
> performance drops until it flatlines from 32MB on at 5000 to
> 7000KB/sec throughput.  This drop does not occur on either server
> running the tests locally, which shows the drop is not due to memory
> caching or controller caching.  Additionally, SMB reads stay constant
> at around 50 to 60,000KB per second.
> I ran ethereal and found one surprising difference between the 16MB
> and 32MB transfers.  For approximately .8 seconds before the transfer
> begins, the following conversation occurs over and over:
> 
> Windows>Linux Write AndX Request
> Linux>Windows Write AndX Response
> Windows>Linux Trans2 Request, QUERY_FILE_INFO, FID: 0x212a, Query File
> Standard Info
> Linux>Windows Trans2 Response, QUERY_FILE_INFO
> 
> I have tried all of the recommended SAMBA performance tweaks that I
> can find, but none seem to affect this dropoff.  Has anyone seen this?
> It appears to be a bug in either Samba or Windows 2003.
> 
> Thanks,
> David
> 
> HEWLETT PACKARD COMPUTER: ProLiant DL380 G3 
> Dual P4 2.8 GHz Xeon Socket Processors with 512KB cache (FULL
> processor speed) 
> 1GB RAM PC2100 DDR SDRAM 200MHz
> 400MHz System Bus Speed
> Dual NC7781 PCI-X Gigabit NICs
> Integrated 5i Plus 64MB cache 
> RAID 5 Hard disk array: 6x 146GB 1.0" Hot-Plug Universal U320 SCSI 10K
> RPM
>