On 06/17/2013 11:11 AM, Nathan Scott wrote:
ok, I have a simple reproducer. try out the following, noting you'll obviously have to change the directory pointed to by dname: libc=ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True) falloc=getattr(libc, 'fallocate')This is using the glibc fallocate wrapper - I have vague memories of an old libc which used to do per-page buffered writes providing a poor-mans implementation of fallocate, maybe somehow that older version/behaviour is being triggered.
Python probably tipped you into a posix_fallocate() bog hole - it writes one byte to every block in the range offset .. offset+len as the portable (but poor-man's) implementation of fallocate(). This combined with your controller cache could explain the unexpected i/o. See glibc:sysdeps/posix/posix_fallocate.c -- Mark _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
