User's Manual

Chapter 6 Storage Screens
NSA-2401 User’s Guide
133
For example if you originally have two disks configured in a RAID 1 array, and you then buy
two more disks and want to configure all four at RAID 5, you should first back up all your data
on those disks (see the Genie Backup Manager utility on the included CD) and then restore
your data later after you create the new array.
Below is a table that summarizes some attributes of the various array levels as supported on
the NSA. For capacity and storage efficiency, “S” is the size of the smallest drive in the array,
and “N” is the number of drives in the array.
Performance rankings are approximations.
The following is a guide to help you choose a RAID level depending on how many disks you
have installed in the NSA. See Section 6.9 on page 151 for technical background on JBOD and
the RAID levels used on the NSA.
One Disk
With only one disk, you must use JBOD. All disk space is used for your data - none is used for
backup. If the disk fails, then you lose all the data on that array. You can later add another disk
to your one-disk JBOD array (without having to re-create shares, access rights and so on) or
create a different JBOD array (and create new shares, access rights and so on).
Two Disks:
You may choose JBOD, RAID 0 or RAID 1. With two disks you could create:
• one or two JBOD arrays
• JBOD gives flexibility and maximum disk space usage. You can later add another disk
to your JBOD array (without having to re-create shares, access rights and so on) or
create a different JBOD array (and create new shares, access rights and so on).
• one RAID 0 or RAID 1 array
• RAID 0 offers higher performance but no data security. It has the fastest read and
write performance since it reads and writes to both disks simultaneously, but if one
disk fails you lose all your data in the array. Performance may matter more than data
security to gamers for example. This method may also be acceptable for data that is
already backed up somewhere else.
• RAID 1 offers data security, although the performance is slower than RAID 0. Since
RAID 1 mirrors data onto a second disk, you can recover all data if one disk fails.
Table 24 RAID Array Levels Quick Comparison
Type of Array RAID 0 RAID 1 RAID 5 RAID 10 JBOD
Number of Disks 2,3,4 2 3,4 4 1,2,3,4
Capacity S*N S*N/2 S*(N-1) S*N/2 sum of disks
Storage Efficiency
A
A. Storage efficiency means what percent of the possible storage capacity can be used. This table assumes all
drives in a RAID array are of identical size. A JBOD array provides capacity equal to the sum of all disks in the
array.
100% 50% (N-1)/N 50% 100%
Fault Tolerance None YYYY YYY YYYY Y
Availability Y YYYY YYYY YYYY YY
Read Performance YYYY YYY YYYY YYYY YY
Write Performance YYYY YYY YY YYY YY