Tuning

In order to achieve a good n2disk setup able to obtain the maximum performance, it is important to take into account the following aspects.

Besides libpcap, n2disk can take advantage from the PF_RING (standard or ZC) acceleration to capture packets from a live network interface.

For ingress traffic rate above 2-3 Gbit/s, PF_RING ZC is recommended. If you have to merge multiple 10 Gbit/s links into a single dumpset, PF_RING FPGA is recommended, using a card that features aggregation in hardware.

In case standard PF_RING is used it is particularly important to reserve enough ring buffer space inside the kernel. Furthermore, in order to reduce the number of clock-cycles needed to capture the packets and cross the network stack, it is possible to turn on quick_mode in the pf_ring kernel module configuration.

For further info about PF_RING and ZC please read the PF_RING documentation.

Regarding the n2disk start-up parameters particularly important are the following options:

  • The buffer length (-b) has to be big enough. 2GB is sufficient in most cases, better to go up to 8GB when the ingress rate is above 10Gbit/s.
  • The write chunk size (-C) has to be greater than or equal to 64 Kbytes, the default value is usually fine.
  • The maximum file size (-p) should not be very small. A good value has to be more than 64 Mbytes.
  • The core binding for the reader (-c) and writer (-w) thread. It is highly recommended to bind those threads to different core of the same physical CPU (according to the system topology, you should choose the physical CPU where the network card is closer/directly connected).
  • If you are using indexing, it is a good practice to enable dedicated indexing threads setting the core affinity (-z <cores> -Z).

Examples

Basic example:

n2disk -i zc:eth1 -o /storage/eth1 -b 8192 -p 1024 --disk-limit 50% -S 0 -c 1 -w 2

Packet indexing enabled:

n2disk -i zc:eth1 -o /storage/eth1 -I -A /timeline/eth1 -b 8192 -p 1024 --disk-limit 50% -S 0 -c 1 -w 2 -z 3,4,5 -Z