ZyXEL NSA-220 User Manual download pdf (Page 66)

Chapter 6 Storage Screens

NSA-220 User’s Guide

lost. Parity protection is used with striping, and the “n” pieces of data are typically the

blocks or bytes distributed across the drives in the array. The parity information can either

be stored on a separate, dedicated drive, or be mixed with the data across all the drives in

the array.

" In the following figures, A1, A2, A3 and so on are blocks of data from the A file.

Similarly, B1, B2, B3 and C1, C2, C3 ar blocks of data from the B and C files.

6.4.1 JBOD

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 multiple different-sized drives into one

big drive. For example, JBOD could convert 80 GB and 100 GB drives into one large logical

drive of 180 GB. If you have two JBOD volumes (with one disk in each), a failure of one disk

(volume) should not affect the other volume (disk). 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 disks in a single JBOD volume. Data is not written across disks but written

sequentially to each disk until it’s full.

6.4.2 RAID 0

RAID 0 spreads data evenly across two or more disks (data striping) with no mirroring nor

parity for data redundancy, so if one disk fails the entire volume will be lost. The major benefit

of RAID 0 is performance. The following figure shows two disks in a single RAID 0 volume.

Data can be written and read across disks simultaneously for faster performance.

Table 16 JBOD

A1 B1

A2 B2

A3 B3

A4 B4

DISK 1 DISK 2

Table 17 RAID 0

A1 A2

A3 A4

A5 A6

A7 A8

DISK 1 DISK 2

1 2 ... 61 62 63 64 65 66 67 68 69 70 71 ... 191 192

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ZyXEL NSA-220 User Manual Page 66