Lesson 01 – SSD and RAID Basics

HDD and SSD Differences

Information storage on most computers is done with a hard drive or HDD. It is a magnetic storage device with 1 or more spinning discs or platters inside. A mechanical arm with a head on the end is used to read data from and write data to the platters.

The two key advantages of hard drives is their capacity to store information and their price. As of summer 2011 you can get a 2TB or 2000GB hard drive for around $80. This makes the price per giga byte of data stored 4 cents for hard drives. You can get a hard drive that can store 3TB of data.

One disadvantage of hard drives is that they are prone to failure. This puts your information in danger of being lost and requires you to regularly backup your data to another disc or online data backup service. The next disadvantage of hard drives is that they are relatively slow at reading and writing data. In modern computers the hard drive is the bottleneck. Chances are if you are waiting for something to happen on your computer, it is because the hard drive can’t keep up. This includes starting Windows, launching a program, moving between screen in a program, etc.

A Solid state drive or SSD is another option for data storage. SSDs have no spinning disk to store data on. All information is written to and read from flash memory chips.

Some of the advantages of SSDs are faster reading and writing of data, faster seek times, low heat production and they are silent. The latest SSDs can read and write data at around 500MBps while hard drives struggle to get to 50MBps. Seek time is the time in Milli seconds a drive takes to get to the next piece of data. SSDs can have seek times as low as .1ms. Hard drives typically have 10ms seek times.

Disadvantages of SSD include low capacities compared to hard drives and a much higher cost per giga byte of storage. SSD capacities as of summer 2011 max out at 1TB while hard drives go up to 3TB in capacity. The cost differences are dramatic. A 1TB SDD is around $3000, while a 1TB hard drive is around $50. For a 128GB SSD the cost is around $230. This make the cost per GB $1.80. Compared to 4 cents per GB on a hard drive, SSDs have a price premium.
Uses for SSDs

On a laptop which typically only has a spot for one drive, if you want the extra speed a SSD can provide you have to sacrifice capacity. On a desktop computer you can use both HDDs and SSDs. The ideal set up is to have an SSD as your boot drive where you install Windows and the majority of your programs.

For your data and lesser used programs you install a HDD. Having Windows and your most used programs on the SSD gives you an extremely responsive experience using your computer. Your data probably consists of personal and work documents, pictures, videos, music, etc. All of which play fine from a HDD or are small enough so that the slower speed of the HDD doesn’t make any noticeably difference.
Drive Interfaces

Modern SSDs, HDDs and DVD or Blu-ray drives connect to the computer through a data cable to a SATA controller on the motherboard. There are two speeds of SATA, SATA 3Gbps and SATA 6Gbps, also called SATA II and SATA III respectively. SATA II’s 3Gbps translates to 375MBps and SATA III’s 6Gbps translates to 750MBps. These are theoretical speeds. Drive speeds are typically measured in MBps. Even the fastest SSD when running on a SATA II controller maxes out at 280MBps when reading and 260MBps when writing. To get past these limits you will need a SATA III drive and a SATA III controller on your motherboard.
SSD form factors

Most SSDs are packaged like 2.5” hard drives and connect to the system using a SATA data cable. The 2.5” size makes them ideal for installation in a notebook computer, which takes 2.5” drives. 3.5” SSDs are available but not easy to find. There is a much greater variety of 2.5” drives drives available. To install a 2.5” drive into a desktop computer you will need a 2.5” to 3.5” adapter. You can find them at most local computer stores and online stores for between $5 and $15. This one has space for 2, 2.5” drives. Some 2.5” SSD come as a kit with the adapter.

SSDs that come in expansion card form and connect through a PCI Express slot on the motherboard are another option. The PCI Express bus allows for much faster transfer rates than even SATA III.

In Lesson 2 we’ll cover other features of solid state drives and RAID including TRIM support, garbage cleanup, firmware updates, the advantages of using RAID and the different types of RAID.