Samba serving files with *very* long access times

[Mark Hadfield]

I access files on our Cray T3E from my Windows 2000 PC via a Samba share.
One of the volumes on the T3E is managed by Cray's Data Migration facility
(DMF). The majority of the DMF files are stored off-line and restored to
disk as necessary. This operation typically takes 3-5 minutes.

Normally when a Windows 2000 application tries to read data from one of the
off-line files--even if it's just the first few bytes--the applications
hangs and then times out after approx. 75 s. This is not a satisfactory
state of affairs because this a frustratingly long length of time but never
long enough to complete the operation. (BTW until you have used a system
like this you might not realise just how often Windows Explorer peeks at the
first few bytes of its files!)

I have been sufficiently motivated recently to do something about this and
have discovered the following registry key...

HKLM\SYSTEM\CurrentControlSet\Services\LanmanWorkstation
    \Parameters\SessTimeOut

Setting this to 600 s increases the timeout period sufficiently that read
operations are normally completed successfully. This is an improvement in
some ways, but still frustrating because while a read operation is
pending...

 * The reading application hangs and cannot be interrupted (even by the End
Process button in Task Manager)

 * No other application on the PC can access the same share.

The latter is especially irritating. It seems as if any given server-client
connection can handle only one transaction at a time. So my question is: is
this a Samba limitation and can it be avoided?

For curiosity's sake I booted the same PC into Linux (RH 7.2) and connected
to the same shares using smbmount. The result is basically the same: if I
try to read data from an off-line file then no other program can access the
same share until the read operation is completed. (I didn't investigate the
time-out period--but it's several minutes--and I didn't investigate whether
a process that's hung in this way can be killed.)

Sorry I don't have much info about the server's Samba configuration because
I'm a mere user. But I'm sure my sysadmin could supply any relevant info if
necessary.

---
Mark Hadfield
m.hadfield at niwa.cri.nz  http://katipo.niwa.cri.nz/~hadfield
National Institute for Water and Atmospheric Research