Let me first explain some of the terminologies
1) the type of physical hard disks
Desktops and workstations usually use 3.5in hard disks, which come in the following interfaces:
- a) Ultra-ATA(parallel Advanced Technology Attachment, also known as IDE or EIDE) drives. Ultra-ATA 100 supports the transfer rate of 100M/s and has the capacity as large as 750GB for a single drive. These are used in old desktops, and have been replaced by SATA drives for better performance. Price: 750G for $120.
- b) SATA(serial-ATA) drives. Currently, SATA-II(or SATA-300) supports a transfer rate of 300M/s (raw bandwidth 3G/s) and the capacity as large as 1TB (Seagate will release a 1.5TB drive soon). Price: 1TB for $200.
- c) SCSI(Small Computer System Interface) drives. Most commonly ones found on market is Ultra-320 (supports 320M/s) and 300GB in capacity. Price: 300GB for $200.
- d) Fiber-channel drives. Common ones on market are FC-AL (Arbitrated Loop) 2G/s (200M/s transfer rate), 300GB for $585.
- e) SAS (Serial Attached SCSI), current 3Gbps models support transfer rate of 375M/s. Price 300GB for $188.
- f) Infiniband, this is relatively new and rare and extremely expensive.
2) Connection type
- a) external or internal: usually the desktop computers and workstations have limited space inside the main case, limited power connectors, motherboard connectors which limit the number of hard drives put inside. For instance, for normal desktops, 4 sata drives are usually at its maximum. Supermicro workstations can put 8 drives inside. So, if you want bigger storage, an external disk array (including rackmount) is recommended. If we choose an external array, all you need is a (external) connection port from the main workstation/server. You then need a PCI adaptor if the motherboard doesn't come with one.
- b) connection bus. Besides the type of drives mentioned above, we can also connect the external drives with FireWire or USB. The number of drives and the connection speed is summarized in wikipedia, and is copied here:
Name  | Raw bandwidth (Mbit/s) | Transfer speed (MB/s) | Max. cable length (m) | Power provided | Devices per Channel |
|---|---|---|---|---|---|
| SAS | 3000 | 375 | 8 | No | 4 |
| eSATA | 3000 | 300 | 2 with eSATA HBA (1 with passive adapter) | No [11] | 1 (15 with port multiplier) |
| SATA 300 | 3000 | 300 | 1 | No | 1 (15 with port multiplier) |
| SATA 150 | 1500 | 150 | 1 | No | 1 per line |
| PATA 133 | 1064 | 133 | 0.46 (18 inches) | No | 2 |
| FireWire 3200 | 3144 | 393 | 100; alternate cables available for 100 m+ | 15 W, 12–25 V | 63 (with hub) |
| FireWire 800 | 786 | 98.25 | 100[12] | 15 W, 12–25 V | 63 (with hub) |
| FireWire 400 | 393 | 49.13 | 4.5[12][13] | 15 W, 12–25 V | 63 (with hub) |
| USB 2.0 | 480 | 60 | 5[14] | 2.5 W, 5 V | 127 (with hub) |
| Ultra-320 SCSI | 2560 | 320 | 12 | No | 16 (HBA is a device) |
| Fibre Channel over copper cable | 4000 | 400 | 12 | No | 126 (16777216 with switches) |
| Fibre Channel over fiber | 10520 | 2000 | 2–50000 | No | 126 (16777216 with switches) |
| Infiniband 12X Quad-rate | 120000 | 12000 | 5 (copper)[15][16] <10000> | No | 1 with Point to point Many with switched fabric |
OK, we can decide what kind of storage system is good for us. Infiniband, Fiber-Channel, SAS are relatively new and expensive. The common solutions currently are either SCSI or SATA. SCSI has been tested for more than 20 years for its reliability and availability. Many businesses still prefer SCSI for mission critical appliations. SATA drives are relatively new. But due to its price and performance, it has gained more commercial market. In another aspect, external SATA 3.0Gbps drives may be connected to SAS backplanes, or Firewire, Infiniband buses.
I will prefer SATA drives because 1) it's big (1TB each drive); 2) it's cheap; 3) the flexibility of connections. I will focus on SATA drives below.
If you want to put SATA drives inside the workstation, notice that normal motherboard only supports 4-6 SATA ports, you will need another SATA adaptor or port multiplier(can also mounted as a PCI card). Also, there are limited SATA power connectors. You can buy IDE to SATA power connector with splitters(usually a few dollars). But make sure that you have a big power supply.
For external drives, there are commercial disk arrays which comes with either eSATA, ethernet, SAS, Firewire, USB interfaces. If speed is not the first priority, for instance, backup devices, you can take Firewire, USB, or ethernet interfaces. Otherwise, you want these external drives run as fast as internal drives, choose eSATA or SAS.
I will discuss how to connect SATA arrays in next blog.
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