I/O errors seen on programs passing via cygwin under heavy stress
Thu May 14 10:06:00 GMT 2009
I am routinely having problems with programs compiled and running via cygwin if they are
using network shares and the level of I/O stress is high.
In a typical case, I have a single Windows Server 2003 node with a single share open to all,
and 3 Windows Server 2003 clients each running an up-to-date cygwin who have mounted the share
via a mount //<ip address>/<share> /test.
On each client I compile and set off the ping_pong locking test which does byte level locking -
so far so good. If on one of those clients I then set off a heavy load generator compiled and
running within the cygwin environment e.g. iozone, the ping_pong tests start reporting
'permission denied' and 'write failed'. iozone itself will generally fail with a write error
I have similar issues when using a range of other tests, including when using Samba on Linux
as the back end server. I have tested with different systems and different networks and seen
the same result. However, if the load generator is a Windows native application, the
problem is not seen.
It looks to me as if the cygwin environment has problems if the I/O traffic becomes "excessive".
Note, if the application tries a retry of a failed write after a short delay, it will generally
succeed, reinforcing my suspicions.
Googling and looking at the mail archives didn't seem to throw up anything similar, however.
Is this a known issue ? Are there ways of tuning the cygwin I/O subsystem ?
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