Reading Journal Week 4 Storage - echadbourne/ChadbourneSYS-140 GitHub Wiki

Storage Devices Ovreview:

• This section gave an overview of the different types of storage devices that one could use. These include optical media, flash media, and magnetic media. The cloud was also covered. The “cloud” is essentially a group of physical storage in a remote location that devices like phones are able to download data to.

My Response:

• I had never really thought about what the “cloud” is and how it works. It was really interesting to learn that the cloud is really just a remote storage system somewhere. I knew it had to be something like that, but it was still interesting to learn about.

Hard Drive Overview:

• Hard Drives are storage devices for data, and can be external or internal. They can “…store more data than flash drives and move data faster than tape drives.” (Hard Drive Overview, Paragraph 1). There are different sizes (aka “form factors”) of hard drives for different uses, including 5.25 inch and 3.5 inch for small servers and desktops, 2.5 inch for laptops and ultrabooks, and 1.8 for ultrabooks and small portable devices, in addition to external models.

My Response:

• I had no idea that they came in so many different sizes. I would love to see a hard drive inside a laptop, since they have to be so small. What kind of storage is used in phones? Hard drives would be too big. Also, I wonder what type of storage device a hard drive is; is it magnetic? How does that work?

SSD Overview:

• A Solid State Drive (SSD) is a type of memory device that uses DRAM or flash memory in place of hard drives. They most commonly use flash memory because they are quieter, faster, and more reliable. There are also Hybrid Solid State Drives (SSHD) which use both flash memory and hard drives. Data is written differently on SSDs than hard drives, involving erasing and moving data to make room for writing data. Write amplification is the minimum amount of data that needs to be erased for a write request to happen. Wear leveling is a method used for erasing that data, but it uses all of the memory blocks instead of just one repeatedly.

My Response:

• The basic concept of SSDs make sense to me, and how they are different from hard drives. I feel that these are more likely used in smaller and lighter devices than hard drives are. In terms of my understanding, the overview of SSDs and SSHD makes sense, but the erasing and moving and writing of data does not. I tried to reword some of the terms to make more sense to me but it only helped a little.

Hard Drive Interfaces Overview:

• A hard drive interface is a set of rules that are in charge of how the hard drive communicates with the rest of the computer. The two main ones are integrated drive electronics (IDE) - aka ATA or EIDE, also most commonly seen in office and home computers - and Small Computer System Interface (SCSI) - most common in network servers. There are two different architectures of these, parallel (not used as much anymore) and serial (more common). In parallel architectures “multiple bits are sent over multiple paths” (Paragraph 3) and in serial architectures they are sent one at a time over one path. The images below show parallel and serial architectures respectively.

My Response:

• The first thing that came to my mind when I saw the image of the parallel architecture was the GPIO pins in the raspberry pi, which can use wiring like you see in the parallel image to run things from the GPIO pins. They look really similar, but I don’t think they are the same, however I wanted to mention it anyway. In addition, it seems counter-intuitive to me that the serial architecture would be better, since in my mind moving multiple bits of data at the same time would be faster, so I would love to know more about how that works.

Hard Drive Preparation Definitions:

• A cluster is made up of sectors, and is the smallest amount of space that is reserved for a single file on the hard drive. An image below shows sectors and clusters. A sector is the smallest amount of storage space that is possible on a platter or disk. It holds 512 bytes of data. A cylinder is a “corresponding track on all surfaces of a hard drive” (Magnetic Hard Drive Geometry Paragraph 4) and is illustrated in the second image below.

My Response:

• I had to do some searching because I could not find the definitions of the requested terms in the section that was indicated, but I was able to find them in the end. I feel like these things will make more sense when I look at a physical hard drive in person, because right now they feel a little abstract.

Fault Tolerance:

• Fault tolerance is “The ability to continue functioning after a hardware or software failure.” In most computers this is achieved through a RAID array configuration of the hard drives. There are different levels of RAID array used for different things, which can be seen in the table below.

My Response:

• It is not clear to me if this is something that is done in all or most computers or if this is just optional and something the user sets up on their own. It does seem that a computer has to be capable of a RAID array before it can be configured though.