If you work in a multimedia field or have very large collections of video files of some sort, large storage arrays become necessary. There are several ways to go about building a multimedia storage array. In this article, we explore one of the possible solutions. We are all waiting for the wonderful new Thunderbolt arrays but they will be expensive and likely will not be available until fall. In the mean time, this is a great eight drive array for a great price.
First off, we need to address connectivity. What type of interface should you be using and what can you use? The answer to this question depends on what system you are using to connect to your storage array. If you are using a Mac Pro or other system with PCIe slots, you have the best options. The fastest readily available way of connecting to an array is eSATA which allows for external SATA II 3Gb/s connections. In addition, some interface cards offer the option of eSATA Port Multiplier support which essentially allows up to five SATA drives in a Port Multiplier-aware enclosure to connect through one cable. This works great but does impose a bottleneck for the drives at somewhere around 300MB/s available for all the drives running through that port. For this article we are only focusing on an eSATA enclosure that support Port Multiplier technology.
For bulk storage a bottleneck of 300MB/s is not all that critical but for day-to-day video editing or other high performance needs it is not ideal. The advent of new SATA III interface cards which operate at 6Gb/s will start to solve this bottleneck and allow upwards of 600MB/s throughput but requires enclosures and drives to support 6Gb/s as well.
As a reference point, USB 2.0 operates at 480Mb/s which works out to be 40MB/s or so at its maximum. FireWire 800 can sustain about double that speed at 80MB/s or so. When talking about those connectivity methods 300MB/s eSATA sounds pretty good. Once again, for most uses it is more than adequate.
Enclosure and Drives
In a market where external drive enclosures tend to be expensive, one company has separated itself from the pack with great value and high quality products. Those are the products of Sans Digital. They have a substantial line of hard drive enclosures. We will focus on a few of their products that fit our needs the best.
Since we are building a storage array, we need space for a number of drives. In our case we want to be able to use eight SATA drives. This brings us to the Sans Digital TR8M eSATA Port Multiplier enclosure for eight SATA drives.
As you can see from the picture there are essentially eight drive sleds that slide into the enclosure. At the back of the enclosure are two eSATA ports that correspond to four drives each using SATA Port Multiplier technology. We are currently using this enclosure with eightHitachi 1TB drives which are currently $60.48. At $0.06 per gigabyte they are a good deal for 7200RPM SATA drives but larger 2TB drives reach a better value.
The current best value for bulk storage is the Hitachi 2TB CoolSpin 5400RPM drive for $79.99 ($0.04/GB). This drive is slower than the Hitachi 2TB 7200RPM drive but those go for $116.34 right now ($0.058/GB). Another option would be the Hitachi 3TB CoolSpin 5400RPM drive drive at $149.99 ($0.05/GB) or the faster Hitachi 3TB 7200RPM drive at $174.99 ($0.058/GB).
In addition to the enclosure and eight hard drives, you will want a fast interface card that supports SATA Port Multiplier technology. By far the best interface card I have used is the Sonnet E4p 4-port eSATA Port Multiplier-aware PCIe x4 card.
This card works great in a Mac Pro and a PC as well. The Sonnet cards in particular seem to get excellent performance with their Marvell chipset. Because of its SATA Port Multiplier support this card actually supports 20 drives if you have the proper enclosures.
The final part of the setup once you have your enclosure, all eight drives, and your interface card is to create your RAID array. In Mac OS X, RAID 0 (striping) and RAID 1 (mirroring) are supported in Disk Utility along with combinations of those such as RAID 10 (stripe of mirrors) and RAID 0+1 (mirror of stripes). Windows also offers software RAID capabilities but we will not address those capabilities in this article. Essentially creating a RAID array allows you to combine the storage space of the drives in different ways to have larger volumes in which to storage your data.
It is important to remember that you do not have to buy all eight drives at once. You can add drives in groups. For example, if you know you need storage now but only need 2TB you could buy two 2TB drives and create a RAID 1 (mirroring) or buy two 1TB drives and create a RAID 0 (striping). In addition, you do not have to use a RAID array at all. It is perfectly possible to leave all eight drives as separate drives and copy data to them individually. You can also mix and match different RAID arrays out of a selection of the drives. We are going to focus on creating a single storage space.
In brief, a two drive RAID 1 creates an identical mirror of your data on two physical drives. RAID 1 is designed to protect you against the failure of a drive. On the other hand, a two drive RAID 0 stripes chunks of your data over both drives. RAID 0 spreads your data out across both drives so accessing it becomes faster but at the cost of protection. If one drive fails everything is gone since most files are spread between both disks.
The combination or nested RAID levels as they are called provide additional protection and performance. RAID 10 or 1+0 is created by taking sets of RAID 1 mirrored drives and striping those together. Let’s say you have four drives. The first two drives would be in a RAID 1 and the second two drives would also be in a RAID 1. Then you would create a RAID 0 with two “drives” that happen to be the two individual RAID 1 sets. This provides the protection of RAID 1 since one drive out of each RAID 1 set can fail but provides the increased performance of RAID 0 by striping the two RAID 1 sets together.
RAID 0+1 is similar to RAID 10 but uses the opposite combination of RAID levels. In this case with four drives you would create two separate RAID 0 arrays and then create a RAID 1 array out of the RAID 0 arrays. The disadvantage in RAID 0+1 is that a single drive cannot fail in both RAID 0 arrays or all data is lost. RAID 10 has the advantage here.
We are currently using a TR8M enclosure with eight 1TB drives in a RAID 10 array which provides 4TB of usable space. We are using this array for backups right now which is why it is setup with a RAID 10 rather than a RAID 0 which would provide 8TB of space. We have been extremely happy with this array and the next step is upgrading it to 2TB or 3TB drives for even more storage. Whether you choose to use RAID 1, RAID 0, RAID 10, or some combination of individual drives and RAID levels, this setup is a very solid one that works great and provides excellent performance and value.