The above diagram shows the ideal SAN based central storage system, and has become something of a 'holy grail' for post-production as in theory it offers the ability to have multiple systems accessing the single central storage without the need to move material between workstations.

But, the reality can be somewhat different if the SAN design is not done correctly.

A major point to make is that a SAN has little to do with the storage - SAN refers to the network used to connect the storage to the various workstations within the facility...

A major issue the storage used can have is with the bandwidth required to allow all the SAN connected systems access to the central storage simultaneously, resulting in a need to reduce the various connections and limit the bandwidth available. As a result, the above system design is rarely able to work as required, with something a bit more like the following being required...

However, even this solution can be limited as there can still be issues with speed of access for the various systems connected to the SAN if they are all accessing a single block of storage simultaneously. The more systems connected, the less speed any one system can maintain, meaning that for 2K (and especially 4K) real-time playback there are serious limits as to how many systems one SAN can support.

In the above diagram the probability is that only one (or possibly two) of the attached systems can maintain real-time 2K playback; and even one system may find it difficult to playback 4K, due to bandwidth limitations of the SAN with all the other systems attached to the same central storage.

So, SANs are often designed with the central storage split into blocks so that more bandwidth control can be provided, but this can mean the 'central storage' is now less central, with different systems accessing different blocks of storage at any given time. Not an ideal situation, as can be seen from the image below, as information will often need to be moved or copied across the storage blocks to enable other system access to it if any one block is to maintain bandwidth necessary to guarantee real-time playback.

Another restriction is the need to limit disc fragmentation, as even a small amount of fragmentation will drastically reduce the available bandwidth. An example is with simultaneous data recording (writing) to the same storage volume, as this will instantly cause fragmentation as the recorded data will never be sequential. So, the used of a renderfarm connected directly to a playback critical SAN is not possible as all renderfarms write fragmented data.

SANs, it appears, are not always the Holy Grail they are often thought to be, although they can be very functional if the limitations are understood and the workflow designed accordingly.

To have any questions answered please send an e-mail to steve@lightillusion.com.