What is a Digital storage device? (External drive & NAS server)
EXTERNAL DRIVE
Now that you have some ideas about internal storage vs. memory after reading Part 1, here in Part 2 I'll talk about the two main types of external storage devices: direct-attached storage (DAS) and network-attached storage (NAS).
DAS and NAS share a few things in common. They both use one or more internal drives (hard drives or SSDs) on the inside, and they utilize the same methods to combine drives' storage space (when multiple drives are used). But before we go any further, let's find out some common terms.
Understanding the common terms
Here are some common terms used when talking about external drives and NAS that you'll likely run into when reading or shopping for storage devices.
Single-volume (single-drive)
This means that the storage device comes with just one internal drive inside. A single-volume external storage device generally has the maximum capacity of its single internal drive, which for now is 4TB or 2TB, depending on the type of internal drive being used, 3.5-inch or 2.5-inch, respectively.
Hosting more than one internal drive not only increases the total storage space but also gives you the option to use RAID.
What is RAID? RAID stands for redundant array of independent disks and requires at least two internal drives. RAID allows for combining multiple drives' storage space into a single volume. Depending on the type of array, a RAID configuration can offer faster speeds, more storage space, or both. Generally, you'll need to use drives of the same capacity in a RAID array. Below are the most common RAID arrays.
RAID 1: Also called mirroring, RAID 1 requires at least two internal drive drives. In this setup, data is written identically to both drives simultaneously, resulting in a mirrored set. A RAID 1 setup continues to operate safely even if only one drive is functioning (thus allowing you to replace a failed drive on the fly). The drawback of RAID 1 is that no matter how many drives you use, you get the capacity of only one. RAID 1 also suffers from slower writing speeds and is mostly used in dual-drive storage devices.
RAID 0: Like RAID 1, RAID 0 requires at least two internal drives. Unlike RAID 1, however, RAID 0 combines the capacity of each drive into a single volume to deliver maximum capacity and bandwidth. The only catch is that if one drive dies, you lose information on all devices. So while more drives in a RAID 0 setup means higher bandwidth and capacity, it also means a greater risk of data loss. RAID 0 is also used mostly for dual-drive storage solutions. Should you chose RAID 0, backup is a must.
RAID 10: This array is used mostly in storage devices that have four internal drives. It's basically a combination of RAID 1 and RAID 0, offering benefits for both performance and data safety.
RAID 5: This array requires at least three internal drives, but it distributes data on all drives while keeping the array safe against the failure of one. Though a single drive failure won't result in the loss of any data, performance will suffer until you replace the broken device. Still, because it balances storage space (you lose the capacity of only one drive in the RAID), performance, and data safety, RAID 5 is the preferred setup.
RAID 6: This array is similar to RAID 5 but now the array can survive the case that two of its internal drive fails at the same time. RAID 6 is generally used in storage devices that have 5 internal drives or more. In a RAID 6, you lose the capacity of two internal drives.
If the above seems complicated, don't feel bad; RAID is quite complicated. The good news is that all RAID-capable storage devices come with the RAID setup preconfigured; most of the time, you don't need to configure it yourself.
Hot-swap: In storage, hot-swap is a feature only available in devices that use a redundancy RAID configuration (i.e. not applicable to RAID 0) and means that you can change one of the internal drives of the array without having to power down the storage device. This is a great feature in case you need to replace a failed drive while still making the storage device available to the host or the network.
In addition to RAID, multiple-drive storage devices usually also offer the JBOD option.
JBOD This is the acronym for just a bunch of disks; in a JBOD setup, each drive works as an individual volume to the host. There's no relationship between them. In other words, if you plug a dual-drive storage device in JBOD to a computer, it will appear as though you plugged in two separate portable drives of the same capacity at the same time.
In addition to the things external drives and NAS devices in common, they also have a few distinctive differences, in terms of connectivity, performance, features, and diversity. These differences give them their own pros and cons.
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