Dispersed Storage Blog

As 2009 comes to a close we thought it was a good time to step back and evaluate larger trends in the industry and what they might mean for storage technology in the coming year. We identified three clear trends which point strongly towards 2010 being a turning point year for networked storage, and in particular dispersed storage. The three primary reasons for this approaching turning point are:

1. With 10 Gbps Ethernet, network speeds have unquestionably eclipsed primary storage speeds
2. Internet access is becoming increasingly ubiquitous, through technologies such as WiMAX, 3G, and LTE
3. Bandwidth is cheap enough that its cost is insignificant compared to the cost of the storage

Network Speed

Most hard drives sold today spin at 7200 RPM and support read and write rates of 80 – 100 MB/s. Special high-performance drives, such as Western Digital’s Raptor drives, have performance up to 150 MB/s. Enterprise grade SAS drives have been able to reach 200 MB/s, and SSD flash drives have achieved speeds between 200 and 300 MB/s. These speeds far exceed the maximum transmission rate of the 1 Gbps Ethernet ports, which can achieve up to 125 MB/s (1 billion bits is 125 million bytes).

Today 1 Gbps Ethernet is common, while 10 Gbps connections are emerging and relatively rare. However, within a few years 10 Gbps will likely be quite common. In what ways might storage evolve as network speed catches up with and overtakes primary storage speeds? 10 Gbps Ethernet is equivalent to 1250 MB/s or 10 times faster than today’s consumer hard drives and 4 times faster than today’s solid state drives.

Today, the hard drive’s role in the computer is that of a fast cache of programs, documents, content, etc. Accessing a movie stored on your hard drive today is much faster than accessing it over the network, but what role will the hard drive serve when that is no longer the case? If streaming a movie from the network could support higher resolutions and frame rates than why stream from a disk? If hard drives and flash are not completely obsolesced by a new much faster storage technology they will have to exist as highly parallelized banks of storage, in which write and read requests are striped across many individual hard drives or SSDs.

If networked storage like this is what the future holds, then information dispersal offers two clear advantages over replication and RAID based systems. The first is that replication works against parallelization in terms of gaining performance. For example, imagine replicating a 1 GB file to five locations. Even though the load is shared across five sites, each site has to handle a full GB of I/O. With dispersal, each location receives only (1 / threshold) of the load, so in a 10-of-15 configuration, each site receives 1/10th of a GB, or 100 MB. Therefore if each Slicestor processed data at 80 MB/s, the set of 15 stores could process data at 800 MB/s (close to the speed of 10 Gbps Ethernet). Notice that the higher the threshold of the configuration, the higher the achievable throughput.

This same advantage applies to RAID systems, in that in a 4+1 RAID 5 array, each disk receives 1/4th the data. However, due to RAID’s limited fault-tolerance, it is dangerous to put too many drives in the same array. Imagine a 20+1 RAID array, it would have the amazing performance of 20 disks reading or writing in parallel, however, if just 2 disks fail out of the 21 in the array there will be data loss. Dispersal can use arbitrarily wide configurations and dial-up the fault-tolerance to match.  For example, a 20-of-25 dispersal configuration could tolerate 5 simultaneous failures, as opposed to the 1 of RAID 5, or 2 of RAID 6.

The second advantage of dispersal offers for networked storage is inherent security and privacy. In a world where computers no longer have built-in hard drives, that means people need to trust their data in the hands of someone else. Not only does this mean the data has to be stored reliability, but it must be stored securely and privately. Dispersal through its SecureSlice(TM) technology ensures that data remains private, and if you don’t trust any single party to hold your data, you could split storage between multiple providers, and neither one could gain enough information to compromise the privacy of your data.

Network Omnipresence

Another trend which is pointing toward network storage is the omnipresence of network connections and Internet access. Airports, hotels, coffee shops, and even grocery stores frequently provide wireless Internet. Many cell phone companies offer Internet access through 3G, and soon a 100 Mbps standard known as LTE will be available. At this speed it becomes possible to stream high definition movies.

If the network is ubiquitous, why should the storage capacity of one’s iPod or cell phone be constrained by the amount of memory that physically fits within that device? Imagine instead of being limited to a few GB in your hand-held device, you could access your entire music or movie collection over the network from anywhere. This is what some companies such as Cablevision are beginning with Network DVR. Access to one’s data would no longer be restricted by what physical things one could take with them.  The potential benefits of network storage combined with network omnipresence are too great to overlook.

Network Cost

The amount it costs to transfer data over the Internet is always falling. Today, depending on location, a network storage provider can purchase a 1 Gbps Internet connection for roughly $7,000 a month. With this amount of throughput, they could transfer 328,717 GB both in and out of the site. This works out to just over 2 cents for each GB written and read.

Assuming the average drive uses about 13.5 watts of power to operate and assuming an electricity cost of $0.12 per Kilowatt hour, it would cost $1.17 a month to power a hard drive. Assuming a 1 TB drive costs $100 and has a useful life of 5 years, the total cost of the drive including capital and operational expenses works out to $2.83 a month.

If instead of using a hard drive, one used network storage and paid 2 cents per GB of transfer, they could write and read up to ($2.83 / $0.02) 141 GB of data per month for less than the price of buying and powering a hard drive. This amount of data is equal to 100 days of listening to MP3s at 1 MB/minute, or 17.1 straight days of streaming movies (assuming 350 MB/hour). Few people watch 400 hours of TV or movies each month, and therefore the cost of the network in network storage is negligible compared to the cost of the storage in the majority of use cases.