Hard Drives, RAID, File Systems, and Optical Media
HDD vs. SSD: Key Differences
A traditional hard disk drive (HDD) is composed of individual disks, or platters, with read/write heads on actuator arms controlled by a servo motor, all contained in a sealed case that prevents contamination by outside air. SSDs use memory chips to store data instead of all those pesky metal spinning parts used in platter-based hard drives. They were originally developed to transition vacuum tube-based technologies to semiconductor technologies. However, they are more expensive than HDDs.
Advantages of HDD vs. SSD: Cooling, Durability, Speed
In an HDD, data is stored in magnetic fields. It converts data in magnetic fields into electrical current. It has multiple platters, and in each platter, there is an actuator arm that has a head at the tip that reads and writes.
In an SSD, data is stored in concentric circles that form a spiral. This spiral is divided into wedges that are formed by clusters, and these by tracks. On the one hand, some of its advantages are that it stores data magnetically, it can be really small as it doesn’t use a motor, and it is very portable. On the other hand, its downside is that it is very expensive, flash memory can only be written a certain number of times, and it has less capacity than an HDD.
Understanding RAID Levels
There are six levels of RAID. Disk mirroring/duplexing is safer but slower than a single hard disk because data is written identically to two drives. At least two drives are required to constitute such an array, and it continues to operate as long as at least one drive is functioning.
- RAID 0 – Disk Striping: Requires at least two drives. It does not provide redundancy to data. If one drive fails, all data is lost.
- RAID 1 – Disk Mirroring/Duplexing: Requires at least two hard drives. RAID 1 is the ultimate in safety, but you lose storage space because the data is duplicated.
- RAID 2 – Disk Striping with Multiple Parity Drives: A weird RAID idea that never saw practical use.
- RAID 3 and 4 – Disk Striping with Dedicated Parity: RAID 3 and 4 combined dedicated data drives with dedicated parity drives. They were quickly replaced by RAID 5.
- RAID 5 – Disk Striping with Distributed Parity: Distributes data and parity information evenly across all devices. This is the fastest way to provide data redundancy.
MBR vs. Dynamic Storage Partitioning
The MBR (Master Boot Record) is a tiny bit of code that takes control of the boot process from the BIOS system in basic disks. The MBR has one task: to look in the partition table for a partition with a valid operating system.
Dynamic disks use an MBR and a partition table, but these older structures are only for backward compatibility. You can use five volume types with dynamic disks: simple, spanned, striped, mirrored, and RAID 5, instead of being limited to four primary partitions.
Advantages of NTFS File System
- NTFS retains copies of its critical file system data and automatically recovers a failed file system, using this information the first time the disk is accessed after a file system failure.
- NTFS offers increased security over the FAT system.
- NTFS supports mirroring drives, meaning that two copies of data can be kept on two different drives to protect against permanent data loss in case of a hard drive crash.
- NTFS uses smaller cluster sizes than FAT, making it much more efficient when using hard drive space.
CD-ROM Layers: Polycarbonate, Aluminum, Acrylic
The polycarbonate plastic layer provides the depth (pits and lands) necessary for the laser. Some parts of the disc will directly reflect the light (lands), while other portions will diffuse the light (pits). Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then, a thin acrylic layer is sprayed over the aluminum to protect the CD from scratches and dust. The label is then printed onto the acrylic.
Tips for Proper CD Care and Handling
- Avoid very high temperatures, humid conditions, and ultraviolet light from sunlight and fluorescent lighting.
- Handle optical discs by grabbing them from the hole in the middle to the edge.
- Fingerprints on a disc might not necessarily harm it, but scratches can cause permanent damage.
- Do not store discs under anything heavy, and do not bend them.
- Mark them with soft-tip permanent markers, and when wiping, do it radially.
CD-ROMs, CD-Rs, and CD-RWs: A Comparison
- CD-ROMs: Opaque and silver. A pre-pressed compact disc that contains data. Computers can read CD-ROMs but cannot write on them. CD-ROMs are popularly used to distribute computer software, including video games and multimedia applications, though any data can be stored (up to the capacity limit of a disc).
- CD-Rs: A recordable compact disc format. The chemicals used to make them produce a brightly colored recording side. Can be recorded in multiple sessions; however, the added information cannot be erased or overwritten. CD-R drives have two speeds that matter: the record speed and the read speed (e.g., burns at 8x and reads at 24x).
- CD-RWs: Look exactly like CD-ROM discs, with the exception of a colored bottom side. This type of CD can be recorded multiple times since the stored data can be deleted. CD-RW drive specs have three multiplier values: the CD-R write speed, the CD-RW rewrite speed, and the read speed (e.g., 8x4x32x).
Why DVDs Store More Data Than CDs
DVDs are able to hold more data because of the material they are made of. DVDs are composed of two layers of polycarbonate, the “data layer.” Also, lands and pits are smaller in DVDs, so the wavelength is shorter.