The NTFS file system have a limited pool of kernel-buffers (lookaside list), which are used when doing file operations ex. a larger read-ahead cache. If there are so many file operations (read/write files), that all the buffers are used up, then it will block for new file operations until an active one have completed.

It is possible to increase the memory usage, so it can handle more concurrent file operations:

[HKEY_LOCAL_MACHINE \System \CurrentControlSet \Control \FileSystem]
NtfsMemoryUsage = 1 (Normal = 1, Increased = 2; Default = 1)

Note the utility fsutil can also be used to change this value:

fsutil behavior set memoryusage 2

More Info MS TechCenter - Fsutil: behavior

Note this setting is mainly for server systems with a high end disk system that consists of multiple disks, which is bombarded with file operations (Like a Web-Server).

Note when increasing the memory usage, then it will use more of both paged- and non-paged-memory. Therefore make sure that existing services/drivers are not already using the available paged and non-paged memory, as these services might perform worse with less memory available.