Technical Reference - ZyXEL Communications NAS326-2T User Manual

5.6 Technical Reference

This section contains background on JBOD and the RAID levels used on the NAS.
JBOD
• Minimum number of disks: 1
• 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.
Table 49 JBOD
A1
A2
A3
A4
DISK 1
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.
Table 50 RAID 0
A1
A3
A5
A7
DISK 1
Chapter 5 Storage Manager
B1 C1
B2 C2
B3 C3
B4 C4
DISK 2 DISK 3
A2
A4
A6
A8
DISK 2
NAS Series User's Guide
97