ZyXEL Communications NAS Series, User Manual

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Chapter 4 Web Configurator Basics
Cloud Storage User’s Guide
69
• Total capacity: Sum of the member disks
• Advantages: Maximum storage capacity, especially for disks of mixed sizes. Flexibility (you can
add disks to the JBOD
• Disadvantages: Not as fast or reliable as RAID.
JBOD allows you to combine multiple physical disk drives into a single virtual one, so they appear
as a single large disk. JBOD can be used to turn several different-sized drives into one big drive. For
example, JBOD could convert 100 GB, 200 GB, 250 GB, and 500 GB drives into one large logical
drive of 1050 GB. Since data isn’t striped across disks, if one disk fails, you should just lose the
data on that disk (but you may lose data in the whole array depending on the nature of the disk
failure). You can add disks to the JBOD array later (using the Add disk to JBOD feature) and even
remove them so JBOD offers a lot of flexibility. However JBOD read performance is not as good as
RAID as only one disk can be read at a time and they must be read sequentially.
The following
figure shows three disks in a single JBOD array. Data is not written across disks but written
sequentially to each disk until it’s full.
RAID 0
RAID 0 spreads data across two or more disks (data striping) with no mirroring nor parity for data
redundancy, so if one disk fails the entire array will be lost. The major benefit of RAID 0 is
performance. The following figure shows two disks in a single RAID 0 array. Data can be written and
read across disks simultaneously for faster performance.
RAID 0 capacity is the size of the sum of the capacities of the disks in the RAID 0. For example, if
you have four disks of sizes 1 TB, 2 TB, 3 TB and 2 TB respectively in one RAID 0 array, then the
maximum capacity is 8 TB.
Typical applications for RAID 0 are non-critical data (or data that changes infrequently and is
backed up regularly) requiring high write speed such as audio, video, graphics, games and so on.
Table 21
JBOD
A1 B1 C1
A2 B2 C2
A3 B3 C3
A4 B4 C4
DISK 1 DISK 2 DISK 3
Table 22
RAID 0
A1 A2
A3 A4
A5 A6
A7 A8
DISK 1 DISK 2