Considerations for IP storage technology

Physical architecture

When building an archive within an existing operation containing standard broadcast systems (e.g. automation, asset management), the archive can generally operate across the same communications infrastructure as the rest of the organization, as long as this contains sufficient bandwidth to accommodate archive transfers.

A recent archive installed by a national broadcaster in Europe across four geographically separated sites used the existing WAN to replicate and centralize archive data.

A combination of 4.5Gb and 1.5Gb connections are able to stream a mixture of HD and SD live feeds and other content, along with an average of around 200TB per month of archived/restored data between the sites. The archive system is also able to schedule transfers, if required, so as not to impinge on live content at busy times.

One item to note on transfer speeds across WANs is that when archiving directly to tape, data transfer speeds have to be kept above a minimum in order not to cause undue stress on tape-drive write heads. Data speeds slower than the optimum for a given tape drive mean that the tape drive has to constantly stop and re-start during the write process, causing a condition known as shoe-shining as the tape slips over the heads; this can impact drive and tape quality and life span. This minimum speed varies with drives, but generally it is recommended to “feed” a drive at no less than 40MB/s.

Size — physical storage

The hardware required for the archive will depend on the agreed-upon levels of provision. Typically, both disk and tape storage will be used, and the total amount will, naturally, depend on the amount of data that is to be processed. However, the size of the archive will be defined not only by standard archive operation considerations (i.e., how much content is moved in a single operation from source to tape or disk), but also on supplemental services (e.g. disaster recovery, content migration), and retention policies.

At our multi-site European broadcaster, the archive cloud handles the 200TB per month of archive/restore data transfers across total disk storage of 600TB, with a DR/deep archive tape library containing 3000+ LTO-5 tapes.

Size — storage control

The next consideration is the controlling application. In our private cloud archive, the content management application sits between the production/management application layer and the storage itself, as shown in Figure 2, and requires its own hardware. The amount of hardware used by the controlling application is directly related to the amount of data throughput that has already been calculated: Depending on the software used, high-end servers may be capable of driving two to five tape drives each, with a data throughput of up to 140MB/s per drive. This is not an exact science, however; concurrent disk and tape transfers, disk cache sizes per server, and, of course, the ever-present spectre of bandwidth are all contributory factors that must be considered.