I've observed a curious problem with our Windows Server 2008 x64 based file server when copying large (~3GB) files from a Windows 7 x64 workstation. The copy becomes extremely slow often proceeding at 100kB/sec or less. Additionally all other SMB file server accesses become really slow including print spooler operations.

Disabling file compression on the target location allows the copy to happen at the limits of the network and disk hardware (~30MB/sec).

The curious behaviour is that there is no apparent cause for the slow down when I go hunting in Performance Monitor. The server CPU is not being used significantly (much less than 1/2 of 1 core on a 4 core CPU), disk queue lengths, disk write times and utilisation, memory, page and non-paged pool, interrupt rates are all similarly very low.

Some details on the server:

  • Dell R300 with a single Xeon X3363 processor and 8GB of RAM
  • Dell MD3000i iSCSI storage with two 1Gbps connections and multi-pathing enabled
  • Main server networking is dual 1Gbps Ethernet in an 802.3ad aggregated link team
  • Does the problem happen when copying < 3GB files? Is this storage internal to the server or external SAN/NAS? – Zero Subnet Dec 2 '13 at 21:10
  • Are you current on your service packs/updates? – Michael Hampton Dec 8 '13 at 17:29
  • I've added some more details on the HW. It's external iSCSI storage that achieves 30MB/sec normally. Smaller files exhibit the problem (so below a threshold like 2GiB). – davefiddes Dec 8 '13 at 17:30
  • What's the server model? – Davidw Dec 8 '13 at 17:42
  • 30MB/s for iSCSI is pretty terrible. That's only about 240Mbps, which is just over 1/4 of what GbE should be able to do with a single path. Are you sure your back-end storage and storage networks are configured properly? – MDMarra Dec 8 '13 at 18:04

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