Xsan: Managing video production workflow in relation to Xsan Volume bandwidth

In a video production workflow that utilizes Xsan, video clips are copied to and from an Xsan Volume. Each copy operation is called a stream. Video production operations that require streaming video include ingest, editing and playout. Each concurrently accessed stream of video consumes a portion of the Xsan Volume’s total minimum available bandwidth. It is important that the video editing workflow be managed so that the total minimum available bandwidth is not exceeded, as doing so may result in dropped frames.

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Calculating an Xsan Volume’s total minimum available bandwidth

A Xserve RAID with 14 drives set up as two 6-drive RAID 5 arrays can handle a minimum of 160 MB of data per second (80 MB/second per RAID controller). Multiply the number of LUNs (arrays) to or from which video will be streamed by 80MB/second to calculate the total minimum available bandwidth.

A Promise VTrak with 16 drives set up as two 6-drive RAID 5 arrays can handle a minimum of 320 MB of data per second. A Promise VTrak with a SAS-connected Expansion Chassis with 32 drives set up as four 6-drive RAID 5 arrays can handle a minimum of 640 MB of data per second.

Note: For optimal performance, configure Promise VTraks using the configuration scripts available here.

Note regarding Xsan: An Xsan volume’s allocation strategy setting and affinities affect how many LUNs video is streamed to and from:

  • The Round Robin allocation strategy copies data to each Storage Pool in a round robin sequence, which typically provides best performance.
  • Writing to an affinity forces data to be written to a single Storage Pool, which may restrict the amount of LUNs to which data is copied.

Calculating your workflow’s required bandwidth

Determine the bandwidth required by your multimedia application by referring to the vendor’s documentation. Since Xsan allows simultaneous access to an Xsan Volume, it’s possible for more than one workstation to access data on the Xsan volume at any given moment. Your workflow determines the amount of simultaneous streams the workstations must simultaneously access.

Calculate your workflow’s total required bandwidth by adding each video stream’s bandwidth that your workstations need to access simultaneously.

Note: Each superimposed layer of video being accessed by a workstation constitutes a stream.

Comparing available bandwidth to required bandwidth

In order to avoid dropped frames errors, the total minimum available bandwidth must be larger than the amount of bandwidth your multimedia application requires.

Example: With video streams from an Xsan volume composed of 10 6-drive Xserve RAID arrays, you could expect a total minimum available bandwidth to be at least 800 MB/second (10 * 80 MB/sec = 800 MB/sec).

If a workflow required at any given moment...

1 ingest stream of Uncompressed SD (10 Bit) = 26.7 MB/sec
1 ingest stream of DCVPRO = 3.43 MB/s
10 edit streams of Uncompressed SD (10 Bit) (26.7 MB/sec * 10) = 267 MB/sec
10 edit streams of DCVPRO (3.43 MB/s * 10) = 34.3 MB/sec
1 playout stream of Uncompressed SD (10 Bit) = 26.7 MB/sec
1 playout stream of DCVPRO = 3.43 MB/sec

...then the workflow’s total required bandwidth would be 361.56 MB/sec. Since the total minimum available bandwidth (800 MB/sec) is greater than the workflow’s required bandwidth (361.56 MB/sec), dropped frames should not occur during the workflow as the result of exceeded bandwidth.

Available bandwidth exceeds required bandwidth but frames drop

If your Xsan volume's available bandwidth exceeds your required bandwidth but you are experiencing dropped frames, see this article.

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