[Samba] 1 byte writes

[Jeremy Allison]

On Wed, Mar 08, 2006 at 07:06:58PM +0100, Thomas Limoncelli wrote:
> After migrating a particular W2K file service to Samba 3.0.21c on SuSE 
> 9.3 Pro (a DMS with winbindd against a W2K3 ADS), the W2K clients are 
> suffering performance issues (in a switched LAN).
> 
> Looking at the traffic with Ethereal (latest SVN), it looks like the 
> client writes the data in *1 byte* pieces likes this (c=client, s=server):
> 
> c->s NT Create AndX Request
> c<-s NT Create AndX Response
> c->s Trans2 Request, SET_FILE_INFO
> c<-s Trans2 Response
> c->s Trans2 Request, QUERY_FILE_INFO, Query File Basic Info (1004)
> c<-s Trans2 Response
> c->s Write AndX Request, 1 byte at offset 119  <-- sigh
> c<-s Write AndX Response, 1 byte
> c->s Trans2 Request, QUERY_FILE_INFO, Query File Standard Info (258)
> c<-s Trans2 Response
> c->s Write AndX Request, 1 byte at offset 155  <-- sigh again
> c<-s Write AndX Response, 1 byte
> c->s Trans2 Request, QUERY_FILE_INFO, Query File Standard Info (258)
> c<-s Trans2 Response
> c->s Write AndX Request, 1 byte at offset 191  <-- see above
> c<-s Write AndX Response, 1 byte
> ...
> c->s Write AndX Request, 1 byte at offset 6629781  <-- 100 secs later!!
> c<-s Write AndX Response, 1 byte
> c->s Trans2 Request, QUERY_FILE_INFO, Query File Standard Info (258)
> c<-s Trans2 Response
> c->s Write AndX Request, 4096 bytes at offset 0  <-- the file header?
> c<-s Write AndX Response, 4096 bytes
> c->s Write AndX Request, 2454 bytes at offset 6627328  <-- strange
> c<-s Write AndX Response, 2454 bytes
> c->s Flush Request
> c<-s Flush Response
> c->s Close Request
> c<-s Close Response
> 
> resulting in incredibly poor write performance. Does this ring a bell 
> with anyone?

What the client is trying to do is extend the file here.

It's writing one byte at increasingly large offsets to
force the filesystem to extend the allocated storage (as
sparse files are rare on NTFS and of course what other
filesystems are there :-). Have you tried playing with
the allocation size ? We normally report it as 1 meg to
stop the clients doing such stupidity.

Jeremy.